US Highway 131 (US 131) is a north–south United States Highway, of which all but 0.67 of its 269.98 miles (1.08 of 434.49 km) are within the state of Michigan. The highway starts in rural Indiana south of the state line as a state road connection to the Indiana Toll Road. As the road crosses into Michigan it becomes a state trunkline highway that connects to the metropolitan areas of Kalamazoo and Grand Rapids before continuing north to its terminus at Petoskey. US 131 runs as a freeway from south of Portage through to Manton in the north. Part of this freeway runs concurrently with Interstate 296 (I-296) as an unsigned designation through Grand Rapids. US 131 forms an important corridor along the western side of the Lower Peninsula of Michigan, running through rural farm and forest lands as well as urban cityscapes. Various names have been applied to the roadway over the years. The oldest, the Mackinaw Trail, originated from an Indian trail in the area while other names honored politicians. An attempt to dedicate the highway to poet James Whitcomb Riley failed to gain official support in Michigan.

Plans to further extend the freeway have either been canceled or placed back under study. Upgrades on the north end through Kalkaska ceased to be considered in 2000. South of Three Rivers, MDOT is studying possible upgrades to US 131. One option for these upgrades is a full freeway, an option that was initially rejected. The preferred alternative in 2008 was a two-lane bypass of Constantine that opened in October 2013.

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