Ōnohara (大野原町 Ōnohara-chō ) was a town located in Mitoyo District, Kagawa Prefecture, Japan.
On October 11, 2005 Ōnohara was merged with the town of Toyohama, also from Mitoyo District, to form the new city of Kan'onji and no longer exists as an independent municipality.
As of 2003, the town had an estimated population of 12,851 and a population density of 248.76 persons per km². The total area was 51.66 km².
Structures of interest in Ōnohara include Honenike Dam, a multiple-arch dam completed in 1930.