1
general::
Phrase(s): one-horse town
Fig. a very small town; a small and backward town. • I refuse to spend a whole week in that onehorse town! • I grew up in a one-horse town, and I liked it very much.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.
American Heritage Idioms