If you're into tenting, there are two campgrounds in the park -- Seawall and Blackwoods.
Seawall Campground ($14 walk-in tent sites; $20 drive-up tent, camper, and motor-home sites) offers 214 campsites, some which meet accessibility needs, all in the woods, all within 10 minutes of the Atlantic Ocean. Roughly half of the sites are available on a first-come, first-served basis; the rest can be reserved through www.recreation.gov . There are no hookups, but there are showers, for a fee, nearby, evening campfire programs in summer, and the campground is on the Island Explorer (see Getting Around section) route. RVs may not exceed 35' (10.7 m) in length and 11' 8' (3.5 m) in height. Extension pull-outs must fit within the site pads provided.
Blackwoods Campground has 306 sites ($20/night May 1-Oct 31; $10 April and November) and accepts reservations at www.recreation.gov from May 1 to October 31. As with Seawall, there are no hookups, showers for a fee are nearby, the campground is served by the Island Explorer, and the ocean is a ten-minute walk away. There are evening campfire programs during the summer. There are restrooms with running water.
A limited number of campsites are available for free primitive camping only in the off season (December 1-March 31) at Blackwoods. Campers must first obtain a permit from the dispatch office at park headquarters (open 8 a.m. to 4:30 p.m. daily). Facilities are limited to a hand pump for water and a portable toilet. The campground entrance road is closed to automobiles during this time; campers are required to hike in from the campground entrance on Route 3. Campers must pack out all trash.
An oft-overlooked part of Acadia is Isle au Haut, a small island southeast of Mount Desert Island. Head there and you'll find the Duck Harbor Campground with its five rustic lean-to sites. You need to land a reservation for these sites, and the application fee is $25, which is returned if they can't fill your request.
Unfortunately, there is no lodging and no camping is allowed on the Schoodic Peninsula, a not-quite 2,300-acre slice of the national park that can be found on the mainland just northeast of Mount Desert Island.
If you manage to bring your horse to the park with you, Wildwood Stables offers a horse camp.