1800
- Sally Sayward Barrell Keating Wood (1759–1855) of York writes the Maine's first novel, Julia, and the Illuminated Baron under the name "A Lady of Massachusetts"
- Portsmouth Naval Shipyard at Kittery opens, oldest naval shipyard continuously operated by the United States Government. It launches its first ship, the 74-gun warship U.S.S. Washington, in 1815
- Population of state reaches 150,000
1804
- Maine Charity School, now Bangor Theological Seminary, incorporates
- Charles Turner (1760-1839) climbs Katahdin, Maine's highest mountain. He records the earliest documented ascent of the mountain
1809
- Settlers in Malta (Windsor) rise up against agents of land proprietors
1813
- USS Enterprise defeats British brig Boxer off the coast of Maine during the War of 1812; Henry Wadsworth Longfellow refers to the incident in his poem My Lost Youth (1858)
- Maine Literary and Theological Institute in Waterville, now Colby College, opens
1814
- British occupy Castine during the War of 1812
1815
- Craftsmen found Maine Charitable Mechanic Association, located in Portland, to support the growing number of artists and artisans in the state
1820
- Maine enters Union as 23rd state on March 15 as a result of the Missouri Compromise that balanced slave and free states. The state's constitution had been adopted a year earlier
- Maine's population is 300,000
- William King of Bath elected as first governor; state capital is at Portland
1822
- Maine Historical Society founded; the third oldest state historical society
1828
- Maine's first and the nation's third African–American Church, the Abyssinian Church in Portland, is founded
1832
- Capital moves from Portland to Augusta, which is more centrally located
1839
- Maine Gov. John Fairfield (1797-1847) declares war on England, resulting in the bloodless Aroostook War, the result of an ongoing dispute about the northeastern boundary of between Maine and New Brunswick
1842
- Webster–Ashburton Treaty establishes the northeastern boundary of Maine and the U.S. with Canada
1843
- After Gov. Fairfield is elected to the U.S. Senate, Maine Senate President Edward Kavanaugh becomes governor, the first Roman Catholic to become governor of a New England state. He serves for nine months, the remainder of Fairfield's term
1844
- African–American Macon B. Allen of Portland practices law in Maine without a license. A year later, he is admitted to the Massachusetts bar, the first African–American to gain that distinction
1847
- Henry David Thoreau (1817-1862) climbs Katahdin and later writes of three trips to Maine in The Maine Woods (published 1893), which ultimately helped promote tourism and conservation in the state.
- Irish immigrants begin arriving in Maine in large numbers, driven out of their home country by the Irish potato famine. They work in industry and construction of roads and canals in a number of Maine communities
