County History
El Paso's County Seat Moved Four Times Before Landing in El Paso City
El Paso County was created in 1850. Its county seat bounced between San Elizario and Ysleta before El Paso city took over for good in 1883.
El Paso County was created in January 1850. The first county seat was San Elizario, a town south of present-day El Paso. The seat moved to Ysleta in 1866, then back to San Elizario in 1868, then to Ysleta again in 1873. El Paso city finally became the permanent county seat in 1883. By then, railroads had arrived and made it the biggest town in the region.
San Elizario, Ysleta, and Socorro all came before the city of El Paso. They grew out of Spanish colonial missions. All three towns were eventually absorbed into modern El Paso. The name El Paso comes from 'El Paso del Norte' — the pass of the north. It describes the natural river crossing of the Rio Grande that people have used for travel for hundreds of years.
Source to confirm: Handbook of Texas — El Paso County