Sauk Trail began as a Native American trail running through Illinois, Indiana and Michigan in the United States. From west to east, the trail ran from Rock Island on the Mississippi River to the Illinois River near modern Peru then along the north bank of that river to Joliet, and on to Valparaiso, Indiana. Then it ran northeasterly to LaPorte and into southern Michigan running through Niles, Three Rivers, Ypsilanti and ending at the Detroit River near Detroit. The trail followed a winding path around natural topography including following the ridges of dune and moraines that mark the earlier glacial period Lake Michigan shorelines. European settlers improved the trail into a wagon road and later into modern highways, although these often have been straightened and rerouted.
There is a suggestion that sections of the trail followed the southern boundary between the dense forest and the mixed grassland regions. The presence of a mastodon trailway along the same path indicates that the Native Americans may have been using a long established game trail. Henry Schoolcraft, at present-day Michigan City, Indiana in 1820, describes the trail, as a "plain horse path, which is considerably traveled by traders, hunters, and others..." and said that a stranger could not follow it without the services of a guide because of the numerous side trails. The Sauk Trail intersected many important trails and early roads including the trails to Vincennes, to Green Bay, to Fort Wayne and to Little Traverse Bay.
Early European settlers used the trail including perhaps Rene-Robert Cavelier, Sieur de La Salle in 1678 to reach Fort Miami, an early fur trade post. Later traders and their Indian suppliers would continue to use the trail. The French and later British militaries used the trail during the time when they occupied Fort St. Joseph. In 1781, the Spanish also used the trail when they raided Fort St. Joseph during the American Revolutionary War.
To better supply the isolated Fort Dearborn in Chicago, the American Congress passed an act to construct a road from Chicago to Detroit. The surveying for this Chicago Road began in 1825 but financial shortfalls led to a decision to mostly follow the path of the Sauk Trail which military couriers were already using. By 1835, daily stage coach departures run by the Western Stage Company traveled all the way from Chicago to Detroit on a multi-day trip whose travel time was dependent on how bad the road was at the particular season. The Chicago Road was described as "a huge serpent, lazily pursuing its onward course, utterly unconcerned as to its destination."
Sections of the trail still exist in some form; for example, the winding road still called Sauk Trail which runs from Frankfort, Illinois to Dyer, Indiana (passing through the town of Sauk Village, Illinois). Johnson Sauk Trail State Park in western Illinois sits on another section of the trail. Sauk Trail forms the southern boundary of Sauk Trail Woods park. When the Lincoln Highway, the first national transcontinental highway was built, its route through western Indiana followed the roads built over the Sauk Trail.
Although called the Sauk Trail after the Sac tribe, other local tribes (such as the Fox, Ho-Chunk (Winnebago), Kickapoo, Potawatomi, Kaskaskia, and Peoria) were known to use it and the trail probably predates Sac presence in the area. The Sac, however, had to travel the entire length of the trail from their home near Rock Island to collect their treaty payments from the British at Fort Malden near Detroit (and later from the Americans at Detroit).
- U.S. Route 12, which follows part of the trail in Michigan
- Saginaw Trail, another trail named after the Sac
- "Old Sauk Trail", Nature Bulletin No. 436-A, December 4, 1971, Forest Preserve District of Cook County
- US 12 Heritage Trail, Western Tour, US 12 Heritage Trail, 2007
- Chicago's Highways Old and New From Indian Trail to Motor Road, Milo M. Quaife, D. F. Keller & Company, Chicago, 1923
- The Chicago Road, Michigan Historical Marker text near Bronson, Michigan
- "The Sauk Trail is still two lanes, narrow, hilly, and winding from South Chicago Heights east to Cottage Grove Avenue, and east from Sauk Village until almost the state line.", Land of Lincolnway Newsletter, Illinois Chapter of the Lincoln Highway Association, June 1995
- Johnson-Sauk Trail State Park, Illinois Department of Natural Resources
- Sauk Trail Woods, Chicago Wilderness Magazine, Gary Mechanic, 2009
- Calumet Beginnings: Ancient Shoreline and Settlements at the South End of Lake Michigan, p.61, Kenneth J. Schoon, Indiana University Press, 2003, ISBN 0-253-34218-X, 9780253342188