The land was once part of Holmanstown Plantation, granted by the Massachusetts General Court in 1789 to Colonel Jonathan Holman of Sutton, Massachusetts (now Millbury) and others.
The plantation’s remaining portion, which had been first settled by Isaac Gleason, was incorporated on February 13, 1818 as the town of Mexico. The name was inspired by local sympathy for Mexico’s 1810–1821 fight for independence from Spain.
Then known as Mexico Corner, it developed as a farming community with mills at the streams.
In 1894, George W. Ridlon, president of the Rumford Falls Brick Company, founded a settlement in the eastern part of the town called Ridlonville.