US Highway 127 (US 127) is a part of the United States Numbered Highway System that runs from Chattanooga, Tennessee, to the Lower Peninsula of the US state of Michigan. In Michigan, it is a state trunkline highway that runs for 214.12 miles (344.59 km), entering from Ohio south of Hudson and ending at a partial interchange with I-75 south of Grayling. Prior to 2002, US 127 ended at I-69 north of East Lansing, a total of approximately 83 miles (134 km).

US 127 is the primary route connecting Lansing and Central Michigan to Northern Michigan and the Mackinac Bridge. From the south side of Jackson northerly, it is mostly a four-lane freeway, with posted speed limits of 70 miles per hour (113 km/h) for passenger cars, and 60 miles per hour (97 km/h) for trucks.

A notable exception is a 16-mile (26 km) stretch from north of St. Johns to just south of Ithaca, where access to the road is not limited and speeds are restricted to 65 miles per hour (105 km/h) for passenger cars, 55 miles per hour (89 km/h) for trucks.

US 127 enters Michigan as a two-lane highway south of Hudson following the course (with minor deviations) of the Michigan Meridian used to survey Michigan in the early 19th century. That stretch is called Meridian Road north to Jackson. From the state line north, US 127 follows the Hillsdale–Lenawee county line north to Hudson and curves east into Addison. North of Addison is the intersection with US 223 at the northern/western terminus of US 223, and about a mile (1.6 km) farther north, US 12 in rural northwest Lenawee County, east of Somerset. US 127 continues northward to the Jackson area where it becomes a full freeway along the east side of Jackson. When US 127 and I-94 meet on the city's northeast side, they join together westward before US 127 splits off northward. The US 127 freeway continues northward through Leslie and Mason to the Lansing area.

In the Lansing area, US 127 follows the I-496/Ransom E. Olds Freeway around the city's east side north of I-96. Right near the Red Cedar River, just west of the Michigan State University campus, I-496 and US 127 separate as US 127 continues north and I-496 turns west. US 127 meets I-69 at the 1998–2002 terminus of the highway. From here north, US 127 follows the former US 27 north to Grayling.

The freeway ends just north of St. Johns. For a 16-mile (26 km) stretch north to just south of Ithaca, US 127 is a four-lane highway with cross-street traffic and driveway access to adjacent homes and businesses. While there are no immediate plans to convert this section to freeway, MDOT continues to purchase parcels for right-of-way to be used for future upgrades.

MDOT has made several improvements to this stretch of roadway recently to improve safety and traffic flow. This includes the construction of an interchange at M-57 in 2000 in southern Gratiot County, replacing an accident-prone intersection. In 2009, MDOT constructed median u-turn crossovers (also known as a "Michigan Left") at several intersections in northern Clinton County to remove cross-street traffic. In April 2010, the MDOT raised speed limits for passenger cars on this non-freeway stretch to 65 miles per hour (105 km/h) from the previous 55 miles per hour (89 km/h).

South of Ithaca, the highway becomes a freeway again for the remainder of its routing. US 127 crosses the Pine River in Alma and runs near the campus of Central Michigan University, crossing the Chippewa River in Mt. Pleasant. Mt. Pleasant is also home to the Saginaw Band of Chippewa Indians and their tribal reservation.

There is a welcome center in the median of US 127/US 10 in Clare. US 127 continues north through the community of Harrison, county seat of Clare County. The freeway serves the resort areas of Houghton Lake and Higgins Lake in Roscommon County before ending 4 miles (6 km) south of Grayling at a partial interchange with I-75. Traffic along US 127 northbound has access to northbound I-75 and southbound traffic on I-75 can access US 127 southbound.

US 127 debuted with the rest of the United States Numbered Highway System in 1926. This new designation replaced part or all of M-14, M-23, M-34 and M-80. US 127 originally ran from the Toledo, Ohio area through Adrian to Jackson and Lansing. The southern end of US 127 was rerouted in 1930 from Somerset south to Hudson and on to Cincinnati, Ohio. The section of former US 127 between Somerset and Toledo became US 223. The city of Mason was bypassed in 1954. The former route through town was designated BUS US 127 at the time. The US 127 expressway was first started in 1957 with an extension south of Mason to Leslie. A further extension to Jackson was opened in 1958. By 1964 this expressway was converted to full freeway, complete with interchanges and the BUS US 127. The US 127 freeway was extended north to the Lansing area by 1968. Near Lansing, it was routed along I-496 to the north side of Lansing and East Lansing to connect with US 27. The last extension of US 127 for another 11 years was completed in 1973 when the freeway was completed north to DeWitt. Two changes took place in the routing of US 127 in the 1980s as the I-69 freeway was completed. The northern Lansing bypass was completed in 1984 and I-69 was built through Clinton County in 1987. These changes routed I-69 along a portion of US 127 near DeWitt and removed a TEMP I-69 routing from US 127 on the east side of Lansing. The opening of the St. Johns Bypass on August 31, 1998 shortened US 127 by almost 2 miles (3 km) while US 27 was routed along the I-69 freeway between exits 87 and 89 to connect with the new freeway northward.

The Michigan Department of Transportation petitioned the American Association of State Highway and Transportation Officials (AASHTO) for approval to remove US 27 from Michigan in 1999. This would remove the 88-mile (142 km) concurrency of I-69 and US 27 south of the Lansing area. MDOT proposed that US 127 be extended north over the former US 27 to Grayling. AASHTO approved this change on April 16, 1999 nearly tripling the highway from 83 miles (134 km) to 214 miles (344 km). The highway markers were changed over in 2002, converting US 27 and the BUS US 27 routes to US 127 and BUS US 127 routes. In 2011, an extra lane was added to the northbound lanes of US 127 between Grand River Avenue at mile marker 78 up to Lake Lansing Road, at exit 79.[citation needed] In 2012, another extra northbound lane was added between the entrance ramp from I-496 and exit 78 at Saginaw Street. MDOT is also expected to construct two auxiliary lanes for the southbound traffic in 2013; one between Lake Lansing Road (exit 79) and Saginaw Street/Grand River Avenue (exit 78), as well as between Saginaw Street and I-496 (exit 76).

The original defined alignment of Interstate 73 (I-73) would have simply run along I-75 to Detroit. However, the definition was amended in 1995 to have a branch along the US 223 corridor to south of Jackson and the US 127 corridor (formerly US 27 north of Lansing until 2002) north to I-75 near Grayling. From Grayling it would simply use I-75 to Sault Ste. Marie. Except south of Jackson, where it is a two-lane road and a section of road north of Lansing where the freeway reverts to a divided highway, this is mostly a rural four-lane freeway. MDOT abandoned further study of I-73 after June 12, 2001, diverting remaining funding to safety improvement projects along the corridor. MDOT included using the US 223 corridor as one of its three options to build I-73 in 2000. The others included using the US 127 corridor all the way into Ohio with a connection to the Ohio Turnpike or using US 127 south and a new freeway connection to US 223 at Adrian. MDOT abandoned further study of I-73 after June 12, 2001, diverting remaining funding to safety improvement projects along the corridor. The department stated there was a "lack of need" for sections of the proposed freeway, and the project website was closed down in 2002. According to press reports in 2011, a group advocating on behalf of the freeway is working to revive the I-73 project in Michigan. According to an MDOT spokesman, "to my knowledge, we’re not taking that issue up again." The Lenawee County Road Commission is not interested in the freeway, and according to the president of the Adrian Area Chamber of Commerce, "there seems to be little chance of having an I-73 link between Toledo and Jackson built in the foreseeable future."