Osceola County is a county in the U.S. state of Michigan. As of the 2020 United States Census, the population was 22,891. The county seat is Reed City. When established by the Michigan Legislature on April 1, 1840, it was named Unwattin County, after Chief Unwattin of the local Ottawa people. As a representative of the Ottawa nation, he participated in n…Osceola County is a county in the U.S. state of Michigan. As of the 2020 United States Census, the population was 22,891. The county seat is Reed City. When established by the Michigan Legislature on April 1, 1840, it was named Unwattin County, after Chief Unwattin of the local Ottawa people. As a representative of the Ottawa nation, he participated in negotiations for the Treaty of Washington that granted a vast expanse of Michigan to the US Federal Government. The name was changed March 8, 1843, to Osceola, after the Seminole chief who achieved renown in Florida.