The Washington County Courthouse is located at 420 South Johnstone Avenue, Bartlesville, OK 74003; phone: 918-337-2830. County Administrative offices are located at 400 South Johnstone Avenue; phone: 918-337-2830.
Washington County was organized in 1907 when Oklahoma became a State. It's territory had formerly been a part of the old Cherokee Nation. Bartlesville was selected as the county seat during the first State Constitutional convention.