Plainville is a village in Adams County, Illinois, United States. The population was 248 at the 2000 census. It is part of the Quincy, IL–MO Micropolitan Statistical Area. In the 1860 Presidential election campaign, Plainville was the site of a political rally involving around 7,000 people. This resulted in the "Stone's Prairie Riot" on August 25, 1860, at which the Republican Party para-military organization, the "Wide Awakes", confronted armed supporters of the Democratic Party.