Portage is a city in and the county seat of Columbia County, Wisconsin, United States. The population was 10,662 at the 2010 census making it the largest city in Columbia County. The city is part of the Madison Metropolitan Statistical 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.