William Jennings Bryan purchased land in the area in 1910, and he established a store and filling station.

[5] According to the United States Census Bureau, the city has a total area of 3.6 square miles (9.3 km2), all land.

As of the 2020 United States census, there were 3,908 people, 1,254 households, and 964 families residing in the city.

6.6% of all households were made up of individuals, and 3.4% had someone living alone who was 65 years of age or older.

Sullivan City is served by the La Joya Independent School District.

The United States Postal Service operates the Sullivan City Post Office.