There are 7 US Post Offices in Canadian County serving a total of 107,113 residents equating to 15,302 residents per post office. It's estimated that approximately 170,964 packages are handled across the 7 county post offices annually. Canadian County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 115,541, making it the fifth-most populous county in Oklahoma. Its county seat is El Reno. The county is named for the Canadian River. Canadian County is also part of the Oklahoma City, OK Metropolitan Statistical Area.