St. Martin is an unincorporated community and former village in Brown County, Ohio, United States.

[5] In November 2011, voters chose to unincorporate St. Martin, and it now falls solely under the jurisdiction of Perry Township.

[6][7] According to the 2010 census, the village had a total area of 1.09 square miles (2.82 km2), all land.

There were 50 housing units at an average density of 45.9 per square mile (17.7/km2).

14.9% of all households were made up of individuals, and 10.7% had someone living alone who was 65 years of age or older.

12.5% of all households were made up of individuals, and 6.3% had someone living alone who was 65 years of age or older.