The Sullivan post office has been in operation since 1843.
Geography
Sullivan is located at . According to the 2010 census, Sullivan has a total area of, all land.
Demographics
2010 census
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. There were 2,110 housing units at an average density of. 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 couplesliving 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. The average household size was 2.27 and the average family size was 2.96. The median age in the city was 39.8 years. 23.8% of residents were under the age of 18; 9.3% were between the ages of 18 and 24; 23.4% were from 25 to 44; 25% were from 45 to 64; and 18.5% were 65 years of age or older. The gender makeup of the city was 46.3% male and 53.7% female.
2000 census
As of the census of 2000, there were 4,617 people, 1,958 households, and 1,176 families living in the city. The population density was 2,410.1 people per square mile. There were 2,264 housing units at an average density of 1,181.8 per square mile. The racial makeup of the city was 97.92% White, 0.50% African American, 0.37% Native American, 0.24% Asian, 0.13% from other races, and 0.84% from two or more races. Hispanic or Latino of any race were 0.82% of the population. There were 1,958 households, out of which 28.5% had children under the age of 18 living with them, 45.0% were married couples living together, 11.6% had a female householder with no husband present, and 39.9% were non-families. 36.0% of all households were made up of individuals, and 19.9% had someone living alone who was 65 years of age or older. The average household size was 2.26 and the average family size was 2.95. In the city, the population was spread out, with 23.5% under the age of 18, 8.9% from 18 to 24, 25.5% from 25 to 44, 22.0% from 45 to 64, and 20.2% who were 65 years of age or older. The median age was 39 years. For every 100 females, there were 83.9 males. For every 100 females age 18 and over, there were 77.5 males. The median income for a household in the city was $26,115, and the median income for a family was $35,042. Males had a median income of $28,773 versus $21,992 for females. The per capita income for the city was $17,717. About 13.6% of families and 16.6% of the population were below the poverty line, including 22.2% of those under age 18 and 11.0% of those age 65 or over.
