Eldridge Post Office. The first post office in Gray County, Eldridge was established on March 20, 1886. The locality was first called Elfin Grove, but the post office was never known by that name. The new facility spared area ranchers a 20-mile ride to Mobeetie to pick up mail. Eldridge Post Office moved in 1888 one mile north of its original site to a spot 1/2 mile west of this location. It stood near a blacksmith shop on McClellan Creek. About 1902 the post office moved several miles south to the railroad, where Eldridge became Alanreed. #1443