Allen County is a county in the U.S. state of Ohio. As of the 2010 census, the population was 106,331. The county seat is Lima. The county was created in 1820 and organized in 1831. The county is named for Colonel John Allen, who was killed leading his men at the Battle of Frenchtown, during the War of 1812. It has also been claimed the county was named for Revolutionary War soldier Ethan Allen, but the weight of the evidence in favor of John Allen led the General Assembly to declare in 1976 that the county was named for him