COUNTY ORGANIZED: 1889
COUNTY NAMED FOR: Robert Anderson Irion, a physician, surveyor, and Republic of Texas secretary of state.
COUNTY SEAT NAMED FOR: M. L. Mertz, a San Angelo banker who was also a director of the Kansas City, Mexico and Orient Railway.
Two - Sherwood in 1901 and Mertzon in 1937.
STANDING: Two - 1901 Second Empire courthouse built of limestone, and the 1937 Moderne courthouse built of brick. The 1901 structure in Sherwood now serves as a community center.