There are 4 US Post Offices in Washington County serving a total of 24,853 residents equating to 6,213 residents per post office. It's estimated that approximately 39,668 packages are handled across the 4 county post offices annually. Washington County is a county located in the U.S. state of Indiana. As of 2010, the population was 28,262. The county seat is Salem. Washington County is part of the Louisville/Jefferson County, KY\u2013IN Metropolitan Statistical Area."