US Highway 12 (US 12) is a US Highway that runs from Aberdeen, Washington to Detroit, Michigan. In the US state of Michigan it runs for 208.90 miles (336.19 km) between New Buffalo and Detroit as a state trunkline highway.

The current US 12 follows roadways that previously carried two other numbers. When the state signposted its State Trunkline Highway System in 1919, the current highway was numbered M-23. After the United States Numbered Highway System was created, US 12 was assigned to replace the original M-17 in the state along Michigan Avenue between Kalamazoo and Detroit, a highway corridor now served by Interstate 94 (I-94). M-23 was replaced by US 112 in 1926. That highway was extended in the 1930s to replace the original M-151. Once the I-94 freeway was completed, the US 12 designation was moved to replace US 112 between New Buffalo and Ann Arbor.

US 12 enters the state of Michigan west of New Buffalo near the town of Michiana. The Lake Michigan Circle Tour is routed along US 12 until the two meet I-94 in New Buffalo. US 12 continues across the southern portion of Berrien County running eastward to Niles. There US 12 meets US 31/St. Joseph Valley Parkway. US 12 runs parallel to the state line intersecting US 131 near White Pigeon and M-66 in Sturgis in St. Joseph County. East of Sturgis, US 12 turns northeasterly to Coldwater and a major intersection with I-69.

East of Coldwater, US 12 runs northeastward to Jonesville northwest of Hillsdale where it meets M-99. In Jackson County it passes near the Michigan International Speedway in Brooklyn. It runs along the Lenawee/Washtenaw county line before turning northeast to Ann Arbor and Ypsilanti. Here it forms Michigan Avenue the rest of the way to Detroit. US 12 and Michigan Avenue part ways briefly in Ypsilanti when US 12 follows I-94 and BUS US 12 follows Michigan Avenue near Willow Run. US 12 runs roughly parallel to I-94 east to Detroit before crossing over to the south side of the freeway and ending downtown Detroit at the corner of Michigan and Cass.

Old US 12 in Michigan runs from downtown Detroit to Chicago. It was replaced by Interstate 94 in 1962, and the state of Michigan re-routed the U.S. 12 designation to the former route of U.S. Highway 112.

What is now US 12 was originally Chicago Road, which ran from Detroit, Michigan, to Chicago, Illinois. It follows the general route of the old Sauk Trail, an important Native American trail. In 1680, the explorer Robert La Salle was probably the first European to travel along it.

The disasters suffered in the War of 1812 taught the Government that it could not defend the western country without roads over which to move its armies and their supplies. In 1824, the United States Congress appropriated money for the survey of roads of national importance in the General Survey Act, and the U.S. President allocated one third of the entire sum to surveying a military highway connecting Detroit with Fort Dearborn at Chicago. From about 1830 on, an ever-increasing flood of settlers poured into the Old Northwest and thousands of them traveled the new highway leading to Chicago, which has ever since been called the Chicago Road. In 1833, the Detroit Arsenal was constructed near the eastern end of the road and its water connection to the East Coast. By 1835, daily stagecoaches ran between Detroit and Chicago.

Construction of the Chicago Road began on the eastern end of the Sauk Trail, and the road did not reach the Michigan-Indiana border until 1835.

It was an old highway that ran through the middle of the major towns and cities of Michigan between Detroit and Chicago. In most cases the road is still there, and is named either Michigan Avenue, Old US 12 or the Red Arrow Highway, named after the 32nd Infantry Division. It is still possible to drive the highway from downtown Detroit all the way to The Magnificent Mile in Chicago, with only a few places in which one is required to navigate around the Interstate Highway. The major break in Old US 12 is in the middle of Michigan in Parma Township . It is at this point that I-94 cuts south to some degree and bisects the old highway, forcing a motorist to navigate north on smaller roads. Some bypassed portions of the roadway have (although faded) dashed white lines,[where?] predating the 1971 Michigan Manual on Uniform Traffic Control Devices.

Prior to 1956, the Detroit-Ann Arbor segment of US 12 was routed directly through Ann Arbor, through Plymouth Township, Livonia, and Redford Township, into Detroit, along the Plymouth-Ann Arbor Road corridor to Plymouth Road's eastern terminus at US 16, Grand River Avenue. US 12 continued on Grand River Avenue, co-signed with US 16, into downtown Detroit. Except for the co-signed Grand River Avenue segment, this route was designated as M-14 when US 12 was rerouted to the Detroit Industrial and Willow Run Expressways, most of which became I-94 in 1962.

Michigan Avenue is one of the major pre-interstate roads of the state of Michigan. Running through the state east to west, it follows the former course of old US 12 which itself followed the earlier military territorial highway, the Chicago Road. Today the Michigan Avenue name follows a discontinuous route: from downtown Detroit to Hayes State Park in Lenawee County it follows the current route of US 12. West of this on the current US 12, the Michigan Avenue name is dropped and the road is known as simply "US 12" (west of the junction with US 127 the road is also known as "Chicago Road").

From the eastern Jackson County boundary west to Battle Creek, it mostly follows the route of old US 12, although it has been routed over newer roads in places where I-94 was built over the former US 12. The Michigan Avenue designation ends on the west side of Kalamazoo, near US 131, and reappears only within the village of Paw Paw.

In Detroit, Michigan Avenue is one of five major avenues (along with Woodward, Grand River, Gratiot and Jefferson) planned by judge Augustus Woodward in 1805 that extend from downtown Detroit in differing directions. Like the other major avenues, the road extends well beyond the city of Detroit, and historically served as a principal axis of expansion for development beyond Detroit and as the main street of many small towns along its route. The road was a principal settlement and trade route to the west, connecting the water route through the Great Lakes from the east to Chicago and the west without the long passage by water around the unsettled North of Michigan.

Historic Tiger Stadium, the home of the Detroit Tigers from 1895–1999, was colloquially named "The Corner", referring to its location on the corner of Michigan Avenue and Trumbull Avenue in Detroit. It has since been demolished.

In Westland, the historic Eloise complex was on Michigan Avenue.

When the original state highway system was signposted in 1919, M-23 ran from the Indiana–Michigan state line near Union to Ypsilanti, and M-17 ran into downtown Detroit. In 1925, US 112 was originally proposed to run from Oshkosh to Fremont, Wisconsin on what later became U.S. Route 110. In 1926, between Edwardsburg and Adamsville, it made a sharp turn to the southwest along what was first US 112S and later until 2002 M-205 in Michigan, then Indiana's State Road 19 and former State Road 112 to connect to US 20 west of Elkhart, Indiana.

The US 12 designation was moved to supplant US 112 in Michigan in January 1962. This removed the US 12 designation from the I-94 freeway except for the Ypsilanti bypass, and US 112 was completely removed as a highway designation. BUS US 112 in both Niles and Ypsilanti became BUS US 12. On March 15, 2001, US 12 was shortened in Detroit by four city blocks to end along Michigan Avenue at Griswold Street. This would be shortened again on June 8, 2005 to Michigan Avenue and Cass Avenue.

Pulaski Memorial Highway, after Kazimierz Pułaski, is an honorary name given to the current routing. It has also been designated as the Iron Brigade Memorial Highway; a designation which it also has in Indiana, Illinois and Wisconsin.

BUS US 12 was a business route running in Niles. It was first designated in 1957 as a business route of US 112. At that time, US 112 and M-60 were transferred to a bypass south of Niles. When US 112 was deleted in 1960, BUS US 112 was redesignated BUS US 12 to match the new US 12 designation. The business loop designation was removed in early 2010. The western terminus of BUS US 12 was at the corner of W. Chicago Rd. and US 12/Pulaski Highway east of the US 12/US 31 interchange. The eastern terminus was at the corner of US 12/Pulaski Highway and M-51 (S. 11th St.).

In 1986, US 33 was truncated in Michigan to end at US 12. BUS US 12 was rerouted in Niles to replace US 33 through town; BUS US 31 was added a year later. The section of BUS US 12 from the US12/M-60 interchange northwest to BUS US 12 along E. Main St. was left as an unsigned trunkline until 1994, when local authorities retained control. In 1998, US 33 was removed from Michigan completely. At this time, M-51 was extended over former US 33 and replaced part of the BUS US 31 designation in Niles.

On March 5, 2010, the segment of BUS US 12 between BUS US 31 and M-51 was turned over to local control. In April 2010 the BUS US 12 designation was retired when an extended M-139 replaced it from the local control section southwestward prior to maps and signage being changed. The concurrent segment along M-51 became M-51 only.

BUS US 12 is a business route running in Ypsilanti. It was first designated in 1962 as a business route of US 12 when US 12 replaced US 112. The western terminus of BUS US 12 is at an interchange with I-94/US 12 south of downtown Ypsilanti. The eastern terminus is at an intersection with US 12 just east of the Wayne/Washtenaw county line. In 1942, Ypsilanti was bypassed by a Bypass US 112 (BYP US 112). US 112 continued to run along its routing in Ypsilanti. In 1956, US 112 was rerouted along BYP US 112, and US 112 through downtown Ypsilanti became BUS US 112, and later BUS US 12.

U.S. Route 112S or US 112S was a spur route of US 112 in the 1930s. Originally, it had been part of US 112 before the latter route was relocated to go through Michigan's southwestern most counties. When US 112 was relocated to New Buffalo, the former US 112 going into Indiana became US 112S. This would continue only a couple of years or so, when the Michigan portion of US 112S would become M-205. In December 2003, the M-205 designation was removed, and today it is a county road.