The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with one-horse town
A small and unimportant place, as in Ours was just a one-horse town until the nuclear plant was built. This expression, first recorded in 1857, presumably alluded to a town so small that a single horse would suffice for its transportation needs.