This is of the style commonly called “Plantation Plain”. This particular house has been stabilized and is a very nice example of this popular 19th-century design. It’s possibly of antebellum origin.
This is one of my favorite places in Effingham County. It was very typical in the early 20th century to find post offices located inside general stores. Joey Smith writes: The Stillwell Post Office was established in 1892. Cletus Gnann served as its postmaster until 1940. Members of his family, Mrs. Frances Gnann and Miss Ethel Gnann, served as postmistresses until 1986, when the Stillwell Post Office was closed. The building was built around 1920. It was a residence, then a general store ( note the old gas pump under the porch on the left), and lastly a post office.