Sorry, but two of the three responses are incorrect. College Park is made up of two separate counties and two zip codes, yet the zip codes cross county lines. Portions are incorporated, yet the majority of the region is not. It also contains a protected historic district and a substantial portion is commercial.
Rebecca, you are in unincorporated Clayton County and your property is zoned residential. Because you are unincorporated, you would need to go through the county zoning and planning. They are located in the old court house in Jonesboro and their phone number is (770) 477-3569.
Best of luck.