Monroe County is a county in the U.S. state of Michigan. As of the 2020 Census, the population was 154,809. The largest city and county seat is Monroe. The county was established as the second county in the Michigan Territory in 1817 and was named for then-President James Monroe. Monroe County is coterminous with the Monroe metropolitan statistical area.

The River Raisin is a river in southeastern Michigan, United States, that flows through glacial sediments into Lake Erie. The area today is an agricultural and industrial center of Michigan. The river flows for almost 139 miles (224 km), draining an area of 1,072 square miles (2,780 km2) in the Michigan counties of Lenawee, Washtenaw, Jackson, Hillsdale, and Monroe County, where its mouth at Lake Erie is located. French settlers named it as La Rivière aux Raisins because of the wild grapes growing along its banks, the French word for grape being raisin. The French term for "raisin" is raisin sec.