Mertzon, the county seat of Irion County, is on Spring Creek, U.S. Highway 67, and the Atchison, Topeka and Santa Fe line, twenty-six miles southwest of San Angelo in the east central part of the county.
It was established as a post office in 1908 and was named for M. L. Mertz, a San Angelo banker who was also a director of the Kansas City, Mexico and Orient Railway, which provided service beginning in 1911. The railroad helped Mertzon develop as the county's largest town by attracting businesses, including two hotels, from nearby Sherwood. The community's population was reported as 550 in 1915, and Mertzon had several churches, a school, a bank, a weekly newspaper, and other businesses. By 1933 the town was incorporated. It carried the county seat election after a spirited contest with Sherwood in 1936. During the late 1930s Mertzon's population peaked at 950, served by some twenty-four businesses. From the 1940s to the late 1970s its population gradually declined, reaching by 1977 a low of 507. In 1988 its population was reported as 837, with nineteen businesses. At that time the town was a ranching and warehouse center for the area. It has benefited from local oil discoveries. In 1990 Mertzon reported a population of 778. The population grew to 839 in 2000.
Mertzon Central School, at the corner of Juanita and Third Streets, is a Recorded Texas Landmark.