Canadian County is a county located in the U.S. state of Oklahoma. As of the 2020 census, the population was 154,405, making it the fourth most populous county in Oklahoma. Its county seat is El Reno. The county is named for the Canadian River, which forms part of its southern border. The river may have been named for early European explorers who were fur traders and trappers from New France, or pre-1763 colonial Canada.