Pomeroy is a city in Garfield County, Washington, United States. The population was 1,425 at the 2010 census. It is the county seat of and only city in Garfield County. Take a look below for 15 fascinating and interesting facts about Pomeroy, Washington, United States. 1. Pomeroy is located at 46°28′24″N 117°35′53″W (46.473334, -117.598119). 2….