There are 13 US Post Offices in Fairfield County serving a total of 133,300 residents equating to 10,254 residents per post office. It's estimated that approximately 212,762 packages are handled across the 13 county post offices annually. Fairfield County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 146,156. Its county seat is Lancaster. Its name is a reference to the Fairfield area of the original Lancaster. Fairfield County is part of the Columbus, OH Metropolitan Statistical Area."