Cynthiana is a town in Smith Township, Posey County, in the U.S. state of Indiana. The population was 545 at the 2010 census. Cynthiana was named for Cynthiana, Kentucky, from whence on September 25, 1815, a group of 44 settlers had come. More settlers from the same area continued to migrate to the area over the following several years. On March 6, 1817, the town was laid out by William Davis, with the plat being recorded on March 17, 1817. It was not until April 22, 1896, that the town incorporated.

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.

A post office has been in operation at Cynthiana since 1820.

The town and northern half of Posey County is served by the MSD of North Posey County which currently operates four schools:
– North Posey High School (9-12)
– North Posey Junior High School (7-8)
– North Elementary School (K-6)
– South Terrace Elementary School (K-6)

Highways
– Interstate 64
– Indiana State Road 68
– Indiana State Road 65