Known locally in Maine simply as "The County," it is the largest American county by land area east of the Rocky Mountains (St. Louis County, Minnesota is larger by total area). As Maine's northernmost county, its northernmost village, Estcourt Station, is therefore also the northernmost community in New England and in the contiguous U.S. east of the Great Lakes.
Aroostook County is known for its potato crops, as well as its Acadian culture. In the northernmost region of the county, which borders Madawaska County, New Brunswick, many of the residents are bilingual (English and French). The county is also an emerging hub for wind power.
Aroostook County was formed in 1839 from parts of Penobscot and Washington counties. In 1843, Aroostook gained land from Penobscot County; in 1844, Aroostook again gained land from Penobscot, plus it exchanged land with Piscataquis County. In 1889, Aroostook gained slightly from Penobscot, but gave back the land in 1903 when Aroostook County gained its final form. Some of the territory in this county was part of the land dispute that led to the "Aroostook War" that would eventually be settled by the Webster–Ashburton Treaty.
The county was also part of a route on the Underground Railroad, and was one of the last stops before entering Canada. Slaves would meet and hide just outside Aroostook or in deserted areas. Friends Quaker Church near Fort Fairfield was often a final stop.
During the post World War II era, much of Aroostook County's economy was dominated by military spending. In 1947, the Limestone Army Air Field was built in Limestone, Maine. It began use in 1953 and was renamed the Loring Air Force Base. Aroostook County was chosen due to its strategic location as the closest point in the Continental United States to Europe. The 1991 Base Realignment and Closure Commission recommended closure of Loring and the Base closed in 1994.
The 2014 Acadian World Congress was held along the Canada–United States border, co-hosted by Aroostook County and a number of neighbouring counties in Canada (Témiscouata in Quebec, and Victoria, Madawaska and Restigouche in New Brunswick). Organizers planned a Tintamarre to be held on the Saint Leonard – Van Buren International Bridge connecting the two countries, as well as a giant tug of war across the Saint John River.