Wilmer is located at the junction of Interstate Highway 45/U.S. Highway 75 and Cottonwood Creek, fourteen miles southeast of downtown Dallas in southeastern Dallas County. Andrew K. Gray, the holder of the original land patent arrived in the area before 1850. The community was called Prairie Valley when the Houston and Texas Central Railroad established a stop in 1872. The earliest of several dates given for the founding of Wilmer is 1876. In 1883 J. W. Johnson, a settler from Tennessee, and later the first postmaster, arrived. In 1884 the post office located in Prairie Valley was renamed Wilmer, after A. J. Wilmer, a conductor on the Houston and Texas Central, who often passed through town.