Downsville is an unincorporated census-designated place in the town of Dunn, in Dunn County, Wisconsin, United States, where Highway 25 crosses the Red Cedar River. As of the 2010 census, its population was 146. The community was founded in 1855. Around that time, Ebenezer Thompson tried to dam the Red Cedar, but his half-built dam was destroyed by a flood. In 1857 Captain Downs tried again and succeeded in building a dam which powered a sawmill.