The Grant County Courthouse in Ephrata, Washington State built in 1917. It was listed on the National Register of Historic Places in 1975. NRHP Ref. #75001850 – Publichall, CC BY-SA 3.0 – Wikimedia Commons Grant County is located in Washington. About 93,259 people live here. Between 2010 and 2020, the population grew from 89,120 to 99,123. The area covers about 7,229.0 square kilometers. The region is divided into 14 Municipalities. The region was founded in 1909. The name originates from Ulysses S. Grant (president of the United States from 1869 to 1877) Grant County is county in Washington, United States. More information at www.co.grant.wa.us.