St. Johns is a city in the U.S. state of Michigan. The population was 7,865 at the 2010 census. It is the county seat of Clinton County. According to the United States Census Bureau, the city has a total area of 3.87 square miles (10.02 km2), all of it land. A mixture of rich forests, plains and farmland (uniquely, mint fields) make up the St. Johns area, providing ample opportunity for outdoor sports and agriculture.