Cynthiana is a town in Smith Township, Posey County, in the U.S. state of Indiana.

[4] On September 23, 1815, Thomas Duncan had made a land entry for the SE 1/4 of Section 11, Township 4 South, Range 11 West of the Second Principal Meridian, receiving a patent to the land on December 20, 1817.

It was on March 24, 1818, that he sold the 58½ acres for the townsite of Cynthiana to William Davis.

[6] According to the 2010 census, Cynthiana has a total area of 0.4 square miles (1.04 km2), all land.

31.4% of all households were made up of individuals, and 14.4% had someone living alone who was 65 years of age or older.

The racial makeup of the town was 98.56% White, 0.43% Native American, 0.29% Asian, and 0.72% from two or more races.

24.5% of all households were made up of individuals, and 12.5% had someone living alone who was 65 years of age or older.