Umatilla is a city in Umatilla County, Oregon, United States. Take a look below for 20 fun and awesome facts about Umatilla, Oregon, United States. 1. The population in 2010 was 6,906, but the city’s population includes approximately 2,000 inmates incarcerated at Two Rivers Correctional Institution. 2. Umatilla is part of the Hermiston-Pendleton Micropolitan Statistical…