St. Johnsis a city in theU.S. stateofMichigan. The population was 7,865 at the2010 census. It is thecounty seat of Clinton County. According to theUnited States Census Bureau, the city has a total area of 3.87 square miles (10.02km2), 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.