There are 10 US Post Offices in Clinton County serving a total of 56,381 residents equating to 5,638 residents per post office. It's estimated that approximately 89,990 packages are handled across the 10 county post offices annually. Clinton County is a county in the U.S. state of Michigan. As of the 2010 census, the population was 75,382. The county seat is St. Johns. The county was created in 1831 and organized in 1839. It is named after early American politician DeWitt Clinton. Clinton County is included in the Lansing-East Lansing, MI Metropolitan Statistical Area."