Topsham is a town in Sagadahoc County, Maine, United States. The population was 8,784 at the 2010 census. It is part of the Portland–South Portland–Biddeford, Maine metropolitan statistical area. The town is home to the annual Topsham Fair.

Called Sawacook, the area was territory of the Pejepscot Abenaki Indians, a subtribe of the Anasagunticooks (now Androscoggins), who controlled the Androscoggin River. They lived and fished at Pejepscot Falls. But a plague, probably smallpox brought by Europeans, decimated the tribe's population in 1615–1616. On June 16, 1632, the area was granted by the Plymouth Council to Thomas Purchase and George Way, later acquired by Richard Wharton, and then in 1714 by the Pejepscot Company.

The first sawmill was built in 1716 on the Cathance River, and in 1717 the plantation received the name Topsham, named for Topsham in Devon, England. On January 31, 1764, it was incorporated as a town by the Massachusetts General Court.Shipbuilding and lumber mills were important early businesses, the latter especially active between 1750–1770. There was a gristmill and brickyard. Pejepscot Falls provided water power to operate mills, and industries included a door, window sash and stairway factory, shingle mill, watch factory, pottery maker, nail factory, pitchfork factory, two tanneries, tobacco manufacturer, two feldspar quarries and a marble works. In 1856, the Sagadahoc Agricultural & Horticultural Society erected its building and fairgrounds, and the town remains host to the annual Topsham Fair.

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