Gainesville was incorporated in 1821 as the seat of newly formed Hall County, named for General Edmund P. Gaines of the U.S. Army. The town grew slowly through the antebellum decades as a foothills crossroads and was occupied by Union forces late in the Civil War. Reconstruction-era rail service connected the town to Atlanta and the upper Piedmont, setting the stage for an industrial and agricultural economy that would later center on poultry processing.
On April 6, 1936, an F4 tornado struck the city center, destroying most of the business district and killing more than 200 people in one of the deadliest tornadoes in U.S. history. President Franklin D. Roosevelt visited the rebuilt downtown in 1938 and dedicated the new square — now Roosevelt Square — at the heart of the rebuild. The poultry industry expanded sharply after World War II, and by the 1960s Gainesville had earned the title of Poultry Capital of the World, an identity still visible in the city's economy and signage.
Two later events reshaped the city: the closure of Buford Dam in 1956, which created Lake Lanier and gave Gainesville a freshwater coastline; and the 1996 Atlanta Summer Olympics, which staged the rowing and sprint-canoe events at Lake Lanier Olympic Park on Clarks Bridge Road. The decades since have shifted the city economy further toward healthcare, higher education, and lake-adjacent residential development.