On May 24, 1825, surveyors began laying out a military road from Detroit to Chicago. The crude road followed the path of the Old Sauk Trail (approximately present-day U.S.12), and upon its completion, two stagecoaches a week operated between Detroit and Fort Dearborn (Chicago).
Sources:
Mich-Again’s Day.
Detroit Historical Society Facebook page
For more information, see U.S. Route 12 in Michigan