The Fox River rises in the Halbach Swamp,[5] 1 mi (1.6 km) southeast of the community of Colgate, Wisconsin[2] and flows past Brookfield, Waukesha, Big Bend, Waterford, Rochester, Burlington, Wheatland, Silver Lake and Wilmot, for a total of 84 miles (135 km)[1] in Wisconsin.

A major dam in Waterford forms a 1,200-acre (4.9 km2) navigable waterway which is one of the busiest in southeastern Wisconsin.

At the southern end of this section, Foxwood Isle separates the main dam to its west and a spillway to the east.

[6] The river enters Illinois where it widens into a large area of interconnected lakes known as the Chain O'Lakes.

Illinois towns and communities that are on the Fox River include (from north to south): Fox Lake, Johnsburg, McHenry, Holiday Hills, Island Lake, Burtons Bridge, Port Barrington, Cary, Fox River Grove, Algonquin, Carpentersville, West Dundee, East Dundee, Elgin, South Elgin, St. Charles, Geneva, Batavia, North Aurora, Aurora, Montgomery, Oswego, Yorkville, Plano, Millington, Sheridan and Ottawa.

In September 2023, the United States Army Corps of Engineers issued a draft report[8] recommending the removal of nine of these dams for environmental reasons.