The county gets its name from a strange underground rock formation

In the early 1850s, settlers near the East Fork Trinity River hit a rock wall while digging a well. The formation ran across the county and sometimes poked up above ground. Some people thought it was a prehistoric man-made structure. Geologists later said it was a natural feature.

The nearby community took the name Rockwall in 1854. When the county was created from Kaufman County in 1873, it took the same name. The rock wall formation is still a local point of interest. The Handbook of Texas documents the discovery and explains its role in naming the county.