CARLA AND JIM BOERMAN of Walworth, N.Y., have been campers for nearly two decades, starting when their twin daughters, who are now in college, were just 18 months old. Their family has stayed in Yellowstone and Yosemite, and they’ve sampled campgrounds in New York and neighboring states, graduating fStaterom pop-ups to small travel trailers to a 30-foot fifth wheel. Last year, the Boermans went on 18 camping trips, for a total of 50 nights under the stars.

But this year, Mrs. Boerman, a school secretary, has noticed something new: campgrounds are fuller, and booking reservations has gotten trickier. “Even if you’re calling months in advance, you might not get the exact campsite you want,” she said, “or you might have to adjust your dates.”

Although it’s still early in the season, there are already signs that more Americans will be vacationing in campgrounds this summer. Bookings are up at many parks — in some cases by as much as 30 percent. And some campgrounds were filled on weekends even before Memorial Day, the traditional kickoff of the camping season.

Many in the camping community believe that the bad economy is causing this sudden interest in the great outdoors, with people who are worried about finances forgoing a stay at a fancy resort or a trip overseas in favor of a sojourn in the woods that can cost 10 bucks a night. Gas prices that are significantly lower than last summer’s (albeit rising) may also be affecting decisions to hit the road.

Suzi Dow, who with her husband, Fred Dow, writes guides to United States Forest Service campgrounds, said that back in April, traffic to their Web site, Forestcamping.com, reached 300,000 hits a day, a rate they don’t normally see until summer, and the queries were decidedly more family-focused.

“In the past, young people, singles, were writing to us saying, ‘Hey, I want to go to Glacier National Park and want to do it in two weeks,’ ” Mrs. Dow said. “Now we’re hearing from families who want to know where to go so their 10-year-old son can go fishing and 13-year-old daughter can have hot showers.”

Although certain parks have always been magnets, camping in general has been declining for a generation, according to the National Park Service. In 1980, there were 3.93 million overnight tent stays at Park Service properties, including the country’s 58 national parks, which contain 861 campgrounds ranging from primitive (pit toilets) to modern (hot showers); last year, 2.95 million stays were registered.

General visitation is down, too, prompting the Secretary of the Interior, Ken Salazar, whose department includes the Park Service, to announce that 147 of its sites would waive entrance fees this weekend and two other weekends this summer (July 18 and 19, and Aug. 15 and 16).

“I’m optimistic,” said David Barna, the chief of public affairs for the National Park Service, whose budget this year increased to $2.5 billion from $2.4 billion last year. This does not count $741 million from the American Recovery and Reinvestment Act of 2009, some of which will go toward campground upgrades like restroom remodeling and the resurfacing of access roads later this year. “Typically, when the economy is not in good shape that bodes well for the park service,” Mr. Barna said.

Indeed, bookings at the 141 national park campgrounds in the National Recreation Reservation Service were up 9 percent from January through March 26 over the same period last year. The reservations are handled by ReserveAmerica, a private company, through the Web site Recreation.gov and at (877) 444-6777 (a fee of $10 is added).

Although many experienced campers booked five and six months ago, when many national park campsites went on sale, the good news for latecomers is that there is still plenty of room at campgrounds that take reservations, particularly during midweek, when demand is lower.

Cancellations do occur, and first-come-first-served campgrounds abound. (Arrive in the morning, when the previous night’s campers are checking out.)

In addition to Park Service properties, there are 5,800 campgrounds in national forests and grasslands, not to mention campgrounds in state parks.

Following is a guide for people interested in scoring a campsite at one of the country’s most popular national parks this summer, along with alternatives if their first choice is sold out. The information was accurate as of June 15.

ACADIA NATIONAL PARK: MAINE
(207) 288-3338; www.nps.gov/acad
Travel Guide

On Mount Desert Island off the Atlantic coast of Down East Maine, this park has rocky beaches, 1930s carriage roads (ideal for hiking and biking) and two wooded campgrounds, both renovated within the last five years.

Campground Status The Blackwoods Campground (207-288-3274; reservations: 877-444-6777 or www.recreation.gov; $20), which is convenient to carriage roads, hiking trails, the Park Loop Road and Bar Harbor, five miles north, takes reservations for nearly all its 290 sites. It is already booked for the Fourth of July weekend but has openings at other times, according to Jennifer Webber, the Blackwoods supervisor.

Seawall Campground (207-244-3600; $14 for walk-ins, $20 for vehicles), on the quieter western side of the park, has 205 sites — tents are separated from RVs — available first come first served. Even during peak camping season — the last two weeks of July and the first two of August — “you have a good chance of getting a spot at Seawall,” said the Seawall supervisor, Don Jenkins.

Also Consider Just across Frenchman Bay from Mount Desert is the 62-site Lamoine State Park Campground (207-667-4778; www.maine.gov/doc/parks; reservations: 800-332-1501 for Maine residents, $15; 207-624-9950 for everyone else, $25; or at www.campwithme.com).

GLACIER NATIONAL PARK: MONTANA
(406) 888-7800; www.nps.gov/glac

By late June, the snow that blankets this million-acre park in the northern Rockies for much of the year is melting, and most of the 13 campgrounds, with 1,009 sites, have opened.

Campground Status All but two of the park’s campgrounds are welcoming guests, with Logging Creek and Quartz Creek slated to open by July 1. The two campgrounds in the park that take reservations (877-444-6777 or www.recreation.gov; $23) — the 178-site Fish Creek Campground, on the west side of the park, and 148-site St. Mary Campground, on the east side — have ample availability.

In this park, the first-come-first-served campgrounds, most of which are smaller than the those that can be reserved, tend to be the most desirable. The Many Glacier Campground ($20) — which offers 109 sites among aspen and pine trees, ranger programs and prime access to trails, including one leading to (you guessed it) a glacier — often fills by 11 a.m. Wondering what your chances are? This park’s sophisticated Web site keeps campers informed with a continuously updated map showing where there are openings, and calendars indicating when each campground has historically reached capacity.

Also Consider The Flathead and Lewis and Clark National Forests (www.fs.fed.us) border Glacier National Park and have campgrounds near the park’s western, southern and eastern entrances. Example: The Big Creek Campground (406-387-3800; $13), in Flathead, two and a half miles from the Camas Creek entrance on the western side of the park, has 22 first-come-first-served sites on the north fork of the Flathead River (garbage must be packed out).

GRAND CANYON NATIONAL PARK: ARIZONA
(928) 638-7888; www.nps.gov/grca
Travel Guide

The 277-mile-long, mile-deep canyon divides the park into two parts: the more accessible, and visited, South Rim, where there are two campgrounds; and the higher-elevation North Rim, which has a single campground.

Campground Status On the South Rim, the 327-site Mather Campground takes reservations (877-444-6777 or www.recreation.gov; $18) and still has openings, but “has been filling up by midafternoon every day,” according to Jim O’Sickey, the deputy fee-program manager for the park. The Desert View Campground ($12) is first come first served, and its 50 sites generally fill by early afternoon. The North Rim Campground takes reservations for its 88 sites (877-444-677 and www.recreation.gov; $18 and $25), but has only a scattering of openings in July, slightly more in August.

Also Consider Kaibab National Forest (www.fs.fed.us/r3/kai) borders Grand Canyon National Park and has campgrounds near park entrances. For example, 4.5 miles from the park’s South Rim entrance, Ten-X Campground (928-638-2443; $10) has 70 primitive sites available first come first served.

On the North Rim, there’s the DeMotte Campground (928-643-7395; $17), with 32 sites five miles from the park (fills between noon and 3 p.m.); and 52-site Jacob Lake Campground, 30 miles from the park, which rarely fills. Both are first come first served and were recently renovated.

GRAND TETON NATIONAL PARK AND JOHN D ROCKEFELLER JR. MEMORIAL PARKWAY: WYOMING
(307) 739-3300; www.nps.gov/grte
Travel Guide

Along with the peaks of the Teton Range, jutting up from a sage-covered plain, the park and the parkway, the eight-mile scenic connection between this park and Yellowstone, have six campgrounds and an RV park, all run as concessions.

Campground Status Flagg Ranch (800-443-2311 and www.flaggranch.com; $25 and $50 a night), a reservation campground five miles north of Grand Teton, has 30 percent of its 86 RV sites available and 70 percent of its 74 tent sites available for July, according to Mike Perikly, the president of Flagg Ranch Resort; bookings are lighter in August.

Of the nonreserved campgrounds, Jenny Lake (800-628-9988 and www.gtlc.com/lodging; $19 and $7), with 59 tent-only sites (10 are for hikers and bicyclists only) among evergreens and glacial boulders near the lake for which it’s named, is the most popular and sometimes fills as early as 10 a.m. The same company runs the 350-site Gros Ventre Campground, and even visitors arriving late at night should be able to find a spot there, according to a park spokeswoman, Jackie Skaggs.

Signal Mountain (800-672-6012; www.signalmountainlodge.com; $20) has 81 sites that typically are occupied by noon.

Also Consider The Caribou-Targhee (in Idaho) and Bridger-Teton National Forests (www.fs.fed.us) border Grand Teton National Park and have campgrounds near park entrances. The campground guidebook author Suzi Dow suggests driving a bit farther, to Granite Creek Campground (307-734-7400; $15), in Bridger-Teton, 45 minutes south of the park, for its 51 first-come-first-served sites near a hot springs-fed pool built into the side of a mountain.

GREAT SMOKY MOUNTAINS NATIONAL PARK: TENNESSEE AND NORTH CAROLINA
(865) 436-1200; www.nps.gov/grsm
Travel Guide

Among the misty mountains of America’s most visited national park — marking its 75th anniversary this year — are 10 developed campgrounds, four of which take reservations.

Campground Status All four reservation campgrounds (877-444-6777 or www.recreation.gov; $14 and $23) — the 142-site Smokemont, the 159-site Cades Cove, the 220-site Elkmont and the 165-site Cosby — are almost fully booked for the Fourth of July weekend, but have openings at other times. All but 20 sites at Cosby, a good jumping-off point for hiking to the Mount Cammerer Fire Tower — with fabulous 360-degree views, rare in this forested park — are first come first served. Balsam Mountain (45 sites), at 5,310 feet, is the coolest spot on hot nights; Deep Creek (92 sites), in North Carolina, offers fishing and tubing; and peaceful Look Rock (68 sites) is ideal for campers who want to string up a hammock and do absolutely nothing.

Also Consider The Cherokee, Pisgah and Nantahala National Forests (www.fs.fed.us) border the national park. Tsali Campground (828-479-6431; $15), in Nantahala, a half-hour from the southern boundary of the park, has 42 unreserved sites, hot showers and a network of mountain-biking trails.

OLYMPIC NATIONAL PARK: WASHINGTON
(360) 565-3130; www.nps.gov/olym
Travel Guide

Thanks to the “Twilight” books — the young-adult series about the romance between a high-school girl and a vampire, written by Stephenie Meyer and set in the Forks, Wash., area — this park has been drawing a new breed of visitor. These “Twihards” wander, wide-eyed, down trails in the misty Hoh rain forest under giant trees festooned with moss, “trying to see what Bella saw,” said a park ranger, Jon Preston. He estimated that at times up to 30 percent of park visitors are Twilight-related and said that he was contemplating putting together a nature program on bloodsuckers (mosquitoes, flies and lampreys).

Olympic has 16 campgrounds, all run by the Park Service.

Campground Status The sole reservation campground, the 170-site Kalaloch (877-444-6777 or www. recreation.gov; $14 to $18), on a bluff overlooking the Pacific Ocean, has only scattered openings. Of the other campgrounds, the 82-site Sol Duc Campground ($14), with a riverside location, great hiking and proximity to the pools at the Sol Duc Hot Springs Resort, often fills by noon. The 88-site Hoh Campground ($12) is right in the rain forest, and, Mr. Preston said, almost always has openings.

Also Consider The Olympic National Forest (www.fs.fed.us/r6/olympic) surrounds the national park. Nine miles from the park’s northwest entrance, the Klahowya Campground (360-374-6522; $17), with 55 spacious, moss- and fern-covered sites, many of them right on the Sol Duc River, is first come first served.

ROCKY MOUNTAIN NATIONAL PARK: COLORADO
(970) 586-1206; www.nps.gov/romo

The chance to ogle “charismatic megafauna”— the elk, bighorn sheep, moose and other large animals that roam within easy viewing distance — is part of the allure of this land of majestic mountains. Five campgrounds await, and sadly, so does a beetle epidemic that has infected forests from British Columbia to Mexico. The park has removed many dead trees and sprayed others, and these continuing efforts will result in fewer campsites this summer, though an exact count has yet to be determined.

Campground Status The two campgrounds taking reservations (877-444-6777 or www.recreation.gov; $20) — the 245-site Moraine Park Campground, in a ponderosa pine forest with Continental Divide views; and the 54-site Aspenglen, bordering the Fall River — are already booked on weekends through July, though there are some openings midweek. There is more availability in August, including on weekends.

Glacier Basin ($20), where many infected lodgepole pine trees have been removed, has opened 61 sites; parts of the 98-site Timber Creek ($20) are expected to open by the end of June. Both these campgrounds no longer have the woodsy character that they did in the past.

But Longs Peak, in the southern part of the park, with 26 first-come-first-served sites for tents only, is as yet unaffected by the epidemic, according to Kyle Patterson, a park spokeswoman.

Also Consider The Arapaho, Roosevelt, and Routt National Forests (www.fs.fed.us) border Rocky Mountain National Park and have campgrounds near park entrances. Five miles from the Wild Basin entrance on the east side of the park is Olive Ridge (303-541-2500), in the Roosevelt National Forest, with 56 sites, half of which can be reserved after June 26 (877-444-6777 or www.recreation.gov).

SEQUOIA AND KINGS CANYON NATIONAL PARKS: CALIFORNIA
(559) 565-3341; www.nps.gov/seki

Groves of giant sequoias are the big draw at these adjoining parks in the southern Sierra Nevada. Overnight stays increased almost 8 percent in 2007, and 5 percent last year. Fourteen campgrounds offer more than 1,200 sites in all.

Campground Status The two campgrounds that accept reservations (877-444-6777 and www.recreation.gov; $20), both in Sequoia, are the largest and busiest: 203-site Lodgepole is fully booked for summer, and 204-site Dorst Creek is fully booked on weekends and 80 to 85 percent on weekdays. But it doesn’t hurt to check for cancellations before your visit and no-shows when you arrive. Tracy Thetford, the revenue and fee business manager, said, “We sell 10 to 15 percent of the sites with daily walk-up sales.” Among the other campgrounds ($12 and $18), the 40-site Potwisha and 28-site Buckeye Flat, which are near the entrance to Sequoia, tend to fill by early Friday evening.

Also Consider The Inyo, Sierra and Sequoia National Forests (www.fs.fed.us) surround the parks, and there are campgrounds in Sequoia National Forest (877-444-6777 or www.reserveamerica.com) convenient to the entrances of both parks (the 90-site Princess, $18, and 74-site Hume Lake, $20, for instance). Eshom (559-338-2251; $18), also in Sequoia, and reached by a narrow, dusty hairpin-turn drive, has 23 first-come-first-served campsites in a former Indian settlement.

YELLOWSTONE NATIONAL PARK: WYOMING, MONTANA, IDAHO
(307) 344-7381; www.nps.gov/yell
Travel Guide

America’s first national park (1872), famous for its steaming hot springs, bubbling mud pots, exploding geysers and roaming grizzlies, bison and elk, has 12 campgrounds. Four of them and an RV park, run by Xanterra Parks and Resorts, take reservations; the Park Service operates the other seven on a first-come-first-served basis. There are 2,100 sites in all, and most of them fill up every night from mid-May through mid-August.

Campground Status The Xanterra campgrounds (866-439-7375 or www.travelyellowstone.com; $18.50) still have ample availability, according to Rick Hoeninghausen, director of marketing and sales for Yellowstone, but “walk-ins have been strong.” The RV park ($35) is almost sold out through the second week of August. The Park Service campgrounds ($12 and $14) often fill by 10 a.m.

Also Consider The Beaverhead, Gallatin, Custer, Caribou-Targhee and Shoshone National Forests (fs.fed.us) surround Yellowstone and have campgrounds on all sides of the park. Three miles from Yellowstone’s west entrance, in Gallatin, is the Baker’s Hole Campground (406-646-1012; www.hebgenbasincampgrounds.com; $14 and $20), which has 73 first-come-first-served campsites and fishing on the Madison River — all that separates the grounds from Yellowstone.

Just southwest of the park, in the Caribou-Targhee National Forest, the Cave Falls Campground (208-652-7442; $10) is rustic and secluded, with 23 unreserved sites a mile from Cave Falls, in Yellowstone’s backcountry.

YOSEMITE NATIONAL PARK: CALIFORNIA
(209) 372-0200; www.nps.gov/yose
Travel Guide

This 1,200-square-mile wilderness in the heart of the Sierra Nevada has 13 National Park Service-run campgrounds containing 1,410 sites. (A 1997 flood wiped out 353 campsites.)

Campground Status The seven that accept reservations (877-444-6777 or www. recreation.gov; $20) — two of them also have first-come-first-served sites — sold out in minutes, as they do every year, when they went on sale five months ago. Cancellations do occur, and no-shows mean that spots at these campgrounds can open up at any time.

But visitors’ best bets are the first-come-first-served campgrounds ($10 and $14). At Camp 4, the only such campground in Yosemite Valley, lines form at 6 a.m. for the 35 walk-in sites. The farther campers go from this prime area, the more likely they are to get a spot as the day wears on. “You have a better chance of getting into Tuolumne Meadows than you do at Tamarack Flat,” Ranger Kari Cobb said.

Also Consider Yosemite National Park is surrounded by the Inyo, Sierra and Stanislaus National Forests (www.fs.fed.us) with campgrounds near entrances on all sides of the park. Three to five minutes from the eastern entrance, in Inyo, are the rustic Lee Vining campgrounds (760-647-3044; $19), including Tioga Lake, with 13 unreserved sites right across the lake from Yosemite.

THE STATE PARK SQUEEZE

All 50 states have park systems of their own, together offering 1,737 camping areas with almost 213,000 sites, according to the National Association of State Park Directors.

Overnight stays increased 12 percent in the year ending June 30, 2008, to 15,486,687, the association, based in Raleigh, N.C., reported. But this total was still well below the peak of 18,011,516 stays in 2003.

This year, budget cuts have forced parks to reduce the days some campgrounds are open, close less popular sections and, in some cases, shut down campgrounds altogether. In New York, for instance, where reservations statewide are up 5 percent over last year, two campgrounds have been closed, and in California, a proposal is under consideration that could result in the shuttering of 220 parks and 56 percent of the state-park campsites.

ReserveAmerica (through www.reserveamerica.com and the company’s call centers) handles campground reservations for 19 states; other states have their own reservation systems. The Missouri State Parks and Historic Sites Web site (www.mostateparks.com/camping.htm), for example, lets you look up campgrounds, then click on photos of actual campsites at some of the parks — not just general campground views — so campers can pick the home away from home that appeals to them most.