Lenawee County is a county located in the U.S. state of Michigan. As of the 2020 United States Census, the population was 99,423. The county seat is Adrian. The county was created in 1822, from territory partitioned from Monroe County. Its governing structure was organized in 1826.

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.