Sullivan is a city in Hamilton Township, Sullivan County, Indiana, United States. The population was 4,249 at the 2010 census. It is part of the Terre Haute Metropolitan Statistical Area. The city is the county seat of Sullivan County.
The Sullivan post office has been in operation since 1843.
Sullivan is located at 39°5′49″N 87°24′23″W (39.096888, -87.406447).
According to the 2010 census, Sullivan has a total area of 1.88 square miles (4.87 km2), all land.
As of the census of 2010, there were 4,249 people, 1,835 households, and 1,073 families living in the city. The population density was 2,260.1 inhabitants per square mile (872.6/km2). There were 2,110 housing units at an average density of 1,122.3 per square mile (433.3/km2). The racial makeup of the city was 97.7% White, 0.1% African American, 0.4% Native American, 0.2% Asian, 0.4% from other races, and 1.2% from two or more races. Hispanic or Latino of any race were 1.4% of the population.
There were 1,835 households, of which 29.4% had children under the age of 18 living with them, 39.2% were married couples living together, 14.3% had a female householder with no husband present, 5.0% had a male householder with no wife present, and 41.5% were non-families. 37.1% of all households were made up of individuals, and 18.1% had someone living alone who was 65 years of age or older.