Portage is a city in and the county seat of Columbia County, Wisconsin, United States. The population was 10,581 at the 2020 census, making it the largest city in Columbia County. It is part of the Madison metropolitan area. Portage was named for the Fox–Wisconsin Waterway, a portage between the Fox River and the Wisconsin River, which was recognized by Jacques Marquette and Louis Joliet during their discovery of a route to the Mississippi River in 1673.