The Thornapple River is an 88.1-mile-long (141.8 km) tributary of Michigan's longest river, the Grand River. The Thornapple rises in Eaton County, Michigan and drains a primarily rural farming area in Central Michigan. It joins the Grand in Ada, Michigan, 10 miles (16 km) east of Grand Rapids.

Kent County is located in the U.S. state of Michigan. As of the 2020 Census, the county had a population of 657,974, making it the fourth most populous county in Michigan, and the largest outside of the Detroit area. Its county seat is Grand Rapids. The county was set off in 1831, and organized in 1836. It is named for New York jurist and legal scholar James Kent, who represented the Michigan Territory in its dispute with Ohio over the Toledo Strip.