Because it’s essentially on the back lot of the L. H. Jackson General Merchandise store, I’m tentatively identifying this as the Jackson Warehouse. It’s likely where feed and other agricultural supplies were stored.
L. H. Jackson General Merchandise was likely the main store in the crossroads community of Lowell, which had a post office from 1878-1903. It is very typical of late-19th and early-20th-century stores in Georgia. The Coca-Cola mural, though faded significantly, is an amazing survivor.