There are 20 US Post Offices in Douglas County serving a total of 361,010 residents equating to 18,051 residents per post office. It's estimated that approximately 576,212 packages are handled across the 20 county post offices annually. Douglas County is a county in the U.S. state of Nebraska. As of the 2010 census, the population was 517,110. It is the state's most populous county, home to over one-fourth of Nebraska's residents. Its county seat is Omaha, the state's largest city. The county was established in 1854 and named after Stephen A. Douglas (1813\u20131861), U.S. Senator from Illinois. Douglas County is part of the Omaha-Council Bluffs, NE-IA Metropolitan Statistical Area. In the Nebraska license plate system, Douglas County was represented by the prefix \"1\" (as it had the largest number of vehicles registered in the county when the license plate system was established in 1922). In 2002, the state discontinued the 1922 system in the three most populous counties: Douglas, Sarpy, and Lancaster counties.