This is from their web site:
Operating Hours & Seasons
Acadia National Park is open year-round. Facilities include Hulls Cove Visitor Center, the Nature Center, Islesford Historical Center, Park Loop Road, two campgrounds, and several picnic areas. For more information about these facilities, choose a category on the left-side menu.
During the winter, some roads and facilities are closed. From mid-November to mid-April, most of the Park Loop Road, including the road to Cadillac Mountain, is closed.
Hulls Cove Visitor Center Hours: Mid-April through June and October, 8 a.m. to 4:30 p.m., daily; July through August, 8 a.m. to 6 p.m., daily; September, 8 a.m. to 4:30 p.m., daily. Closed from November 1 to mid-April.
Winter Visitor Center/Park Headquarters Hours: November 1 to mid-April, 8 a.m. to 4:30 p.m., daily. Closed Thanksgiving Day, December 24 and 25, and January 1. Mid-April to October 31, 8 a.m. to 4:30 p.m. M-F.
From the FAQ section:
Is the road to Cadillac Mountain open to vehicles in the winter?
No. Access is by snowmobile, skis, or on foot. It is a minimum walk of nine miles round trip. Temperatures on Cadillac can be well below zero, with extremely high winds and drifting snow.
Can I hike any of the mountain trails in the winter?
Hiking mountain trails in the winter is not recommended. Trail markers and icy patches are obscured by drifting snow, creating very dangerous conditions for hikers.
Can I rent skis and other equipment nearby?
Skis, snowshoes, and skates can be rented in Bar Harbor. There are no snowmobile rentals on the island.
Other road information:
The Park Loop Road will close on December 1 or after the first major snowfall, whichever comes first.
The one-way section of the Park Loop Road from its beginning just south of Route 233 to the junction with Otter Cliff Road will be closed from 6 p.m. to 7:30 a.m. for wildlife protection. This closure will be in place from October 29 through the month of November.
And some more info on winter activities:
Cross-Country Skiing: Forty-five miles of carriage roads and 41 miles of unplowed park roads are suggested for cross-country skiing and snowshoeing. Skiing on hiking trails is not recommended because of the uneven and steep nature of trails, ice falls blocking the path, and trail routes obscured by snow. Ski equipment and rentals are available in some of the local communities. Ski tracks are sometimes laid down by volunteers on sections of the carriage roads when snowfall exceeds four inches.
Snowmobiling: Visitors trailering their snowmobiles are encouraged to use the Hulls Cove Visitor Center, Sieur de Monts Spring, and Jordan Pond (boat ramp area) parking lots in order to access the Park Loop Road.
Snowmobile travel is allowed on the 27-mile Park Loop Road (except a 1-mile section at Jordan Pond House), and most fire roads. Only two miles of carriage roads are open to snowmobilers as connector trails. The remaining 43 miles are closed to snowmobilers.
Winter Hiking: Acadia's trails become icy and/or snowpacked in winter. Be prepared for unfavorable conditions and early darkness.
Call the park at 207-288-3338 for updates on snow conditions.
) I lived in Bangor too so I think that makes it worse. Going back to Acadia has been on my item for a while and I'd like to go in Winter, or at least a non-summer season. My question is, what is winter access like to the Park? I seem to remember something about road closure during winter. How accessible are things there? Thanks. 
