Dilley is on the Missouri Pacific Railroad and Interstate Highway 35 sixteen miles southwest of Pearsall in far southern Frio County. The community was originally called Darlington, after a local landowner who settled in the area in the mid-1860s. The settlement was established on the International-Great Northern Railroad from San Antonio to Mexico, completed during the early 1880s. At the time Darlington had a general store and several dwellings. The community was sometimes called Ford because of a nearby Frio River crossing of an old Spanish trail, known as Rocky Ford. The I-GN built its first railroad depot, siding, and stock pen near the crossing.