The Comanches were defeated by the United States Army in the Red River War of 1874.

[5][4] In 1876, Charles Goodnight brought a herd of 1,600 cattle into the Palo Duro Canyon, and he and John George Adair established ranching in the county.

The county land use was primarily ranch-related, even after the trickling in of homesteaders, for the remainder of the 19th century.

[6] In 1887, the JA Ranch split up, giving way to a terminus for the Fort Worth and Denver City Railway.

[7] Landowner Robert E. Montgomery platted the town of Washburn, named after railroad executive D.W.

The Great Depression had a severe effect on the county's economy, and recovery took years.

[10][11][12] According to the U.S. Census Bureau, the county has a total area of 914 square miles (2,370 km2), of which 4.7 sq mi (12 km2) (0.5%) are covered by water.

The Armstrong Sheriff's Office no longer operates a county jail, as it was closed in April 2022.

The old Armstrong County Jail, located in Claude, Texas was erected in 1953 with the designs of Lawrence A. Kerr and Clayton B. Shiver.

The jail was also the location of the county's public-safety answering point (PSAP) and dispatch center.