The Fox River is a 202-mile-long (325 km) tributary of the Illinois River, flowing from southeastern Wisconsin to Ottawa, Illinois in the United States. The Wisconsin section was known as the Pishtaka River in the 19th century. There is another Fox River in Wisconsin that flows through Lake Winnebago into Green Bay. There are also two other "Fox Rivers" in southern Illinois: the Fox River (Little Wabash tributary) and a smaller "Fox River" that joins the Wabash River near New Harmony, Indiana.
|• location||1 mi (1.6 km) southeast of Colgate, Wisconsin|
|• elevation||942.78 ft (287.36 m)|
|Illinois River at Ottawa, Illinois|
|460.28 ft (140.29 m)|
|Length||202 mi (325 km)|
|• average||2,346.01 cu ft/s (66.432 m3/s) (estimate)|
|Progression||Fox River → Illinois → Mississippi → Gulf of Mexico|
|River system||Mississippi River|
|• left||Poplar Creek, Morgan Creek|
|• right||Nippersink Creek, Tyler Creek, Ferson Creek, Big Rock Creek, Indian Creek|
The Fox River watershed encompasses 1720 square miles in Illinois and 938 square miles in Wisconsin.
The Fox River rises in the Halbach Swamp, 1 mi (1.6 km) southeast of the community of Colgate, Wisconsin and flows past Brookfield, Waukesha, Big Bend, Waterford, Rochester, Burlington, Wheatland, Silver Lake and Wilmot, for a total of 84 miles (135 km) 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. The river is generally navigable from the Iron Bridge (now a concrete bridge) in Tichigan, Wisconsin (just south of Big Bend) down to the dam. The river connects several small lakes in this section, and one large lake, Tichigan Lake and one smaller lake, Buena Lake. The entire area including connected lakes and the Fox are often referred to as Tichigan Lake.
At the southern end of this section, Foxwood Isle separates the main dam to its west and a spillway to the east.
A small dam is present just a few miles south in downtown Rochester. The river then flows unobstructed through Burlington, where it joins the White River, and on to Wilmot. This is a popular and picturesque day-canoe trip never straying far from the road, but often just out of sight of it.
Flooding is common on this section of the river, especially near Wheatland to the border.
The Fox River watershed encompasses 938 square miles in Wisconsin.
The river enters Illinois where it widens into a large area of interconnected lakes known as the Chain O'Lakes. Fox Lake is the largest village in this area. From the chain, the river flows generally southward for 118 miles (190 km), until it joins the Illinois River at Ottawa. 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. Collectively, the area surrounding the Fox River is known as the Fox Valley. Around 1 million people live in this area.
The Fox River has 15 dams, including McHenry Dam, which raises the river slightly to maintain depth in the Chain O'Lakes in northern Illinois, the Montgomery Dam and the Dayton Dam, a hydroelectric dam near Ottawa. In the winter, bald eagles can be found nesting along the banks.
Early in the history of Illinois, the Fox River provided water for the Illinois and Michigan Canal via a feeder canal, allowing the canal to pass over the Fox River on an aqueduct.
The Fox River watershed encompasses 1720 square miles in Illinois. 
- U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map Archived 2012-03-29 at the Wayback Machine, accessed May 13, 2011
- "Fox River". Geographic Names Information System. United States Geological Survey. Retrieved 15 August 2012.
- United States Environmental Protection Agency. "Watershed Report: Fox River". WATERS GeoViewer. Archived from the original on 2021-08-08. Retrieved 2021-08-08.
- Increase A. Lapham (1855). Ancient Works in The Basin of the Pishtaka River. The Antiquities of Wisconsin. ISBN 9780722203552. Archived from the original on 2016-05-29. Retrieved 2015-09-02.
- Effects of Lowhead Dams on Unionids in Fox River, Illinois
- https://www.lakecountyil.gov/2401/Fox-River-Watershed Stormwater Management Commission, Lake county, Illinois Retrieved 5/24/21
- "Major Watersheds of Illinois" (PDF). Illinois State Water Survey. Illinois Dept. of Natural Resources. 2001. Archived from the original (PDF) on 2011-07-19. Retrieved 2009-03-29.
|Wikimedia Commons has media related to Fox River (Illinois River tributary).|
- Wisconsin Dept. of Natural Resources
- Fox River Paddling/Fishing page
- Friends of the Fox River
- Fox River Ecosystem Partnership (IL)
- Fox River CAUSE (WI)
- Southeast Fox River Partnership (WI)