Lake Wisconsin is a census-designated place in Columbia and Sauk counties, in the towns of Lodi and Merrimac, in Wisconsin, United States. The population was 4,616 at the 2020 census, up from 4,189 at the 2010 census. The Columbia County portion of the Lake Wisconsin is part of the Madison Metropolitan Statistical Area, while the Sauk County portion is part of the Baraboo Micropolitan Statistical Area.