Plainville is a town in Hartford County, Connecticut, United States. The population was 17,716 at the 2010 census. According to the United States Census Bureau, the town has a total area of 25.3 square kilometres (9.8sqmi), of which 9.7 square miles (25.2km2) is land and 0.077 square miles (0.2km2), or 0.72%, is water. The east side of the town is bordered by two prominent peaks of the Metacomet Ridge: Pinnacle Rock and Bradley Mountain. The 51-mile (82km) Metacomet Trail traverses those peaks.