The Harrisburg Commercial Historic District encompasses the historic civic and commercial heart of Harrisburg, Arkansas, the county seat of Poinsett County, located in the far northeastern part of the state. The district encompasses the buildings surrounding Court Square, where the Poinsett County Courthouse is located, and extends a short way north and south on Main and East Streets. Although Harrisburg was founded in 1856, its substantial growth did not begin until after the arrival of the railroad in the 1880s. The oldest building in the district is the Harrisburg State Bank building at 100 North Main. The courthouse is a grand Classical Revival structure built in 1917. Most of the district buildings were built before the Great Depression, using brick or masonry construction.