Map - Monroe County, Michigan (Monroe County)

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 (after Wayne County) in the Michigan Territory in 1817 and was named for then-President James Monroe.

Monroe County is coterminous with the Monroe, MI micropolitan statistical area.

Before the county's formation, the primary settlement was Frenchtown, which was settled in as early as 1784 along the banks of the River Raisin. The small plot of land was given to the early French settlers by the Potawatomi Native Americans, and the area was claimed for New France. The settlement of Frenchtown and the slight northerly settlement of Sandy Creek drew in a total of about 100 inhabitants. During the War of 1812, the area was the site of the Battle of Frenchtown, which was the worst American defeat in the war and remains the deadliest conflict ever on Michigan soil. The site of the battle is now part of the River Raisin National Battlefield Park.

Monroe County was formed from the southern portion of Wayne County in 1817. At the time, the Michigan Territory, which had not yet received statehood, consisted of only Wayne County since Detroit was the only area with a population over 1,000 people. When the area became more populated, the southern portion of Wayne County was broken off to form Monroe County with the settlement of Frenchtown was platted with the name "Monroe". The settlement also incorporated as a village in 1817 and became the county seat of Monroe County. The county and its county seat were named in honor of then-President James Monroe in anticipation for his upcoming visit to the area. Shortly after its formation, Monroe County's population was recorded at only 336 in the 1820 census. When the county was originally formed, it stretched for 60 mi inland (twice its current size), but the western half was split off to form Lenawee County in 1826.

Monroe County's most famous resident, George Armstrong Custer (1839–1876), moved to Monroe as a child and lived with his half-sister and brother-in-law. Although not born in Monroe, he attended school in Monroe and later moved away to attend the United States Military Academy. He returned to Monroe in 1864 during the Civil War to marry Elizabeth Bacon (1842–1933), whom he met while previously living in Monroe. Much of Custer's family resided in Monroe, included Elizabeth Bacon, Henry Armstrong Reed (1858–1876), and Boston Custer (1848–1876). Following their deaths in the Battle of the Little Bighorn, Henry and Boston were interred and memorialized in Monroe's historic Woodland Cemetery, as are many members of Bacon's family. Although dying in the same battle, George Custer was interred at West Point Cemetery, and Elizabeth Bacon was buried next to him when she died many decades later. In 1910, then-President William Howard Taft and the widowed Elizabeth Bacon unveiled an equestrian statue of Custer that now rests at the corner of Elm Street and Monroe Street in the heart of downtown Monroe.