There are 4 US Post Offices in Morrow County serving a total of 10,595 residents equating to 2,649 residents per post office. It's estimated that approximately 16,911 packages are handled across the 4 county post offices annually. Morrow County is a county in the U.S. state of Oregon. As of the 2010 census, the population was 11,173. The county seat is Heppner. The county is named for one of its first white settlers, Jackson L. Morrow, who was a member of the state legislature when the county was created. Half of the Umatilla Chemical Depot, which includes the Umatilla Chemical Agent Disposal Facility, is within the county. Morrow County is part of the Pendleton\u2013Hermiston, OR, Micropolitan Statistical Area. It is located on the south side of the Columbia River and is included in the eight-county definition of Eastern Oregon."