The Old State Capitol is a reconstruction of Illinois's fifth statehouse, the first to be located in Springfield. The building served as the seat of state government and a center of Illinois political life from 1839 to 1876. The first floor is composed of a central hall flanked by rooms interpreting government offices, two libraries, and the supreme courtroom. A complex of first-floor rooms also provides an audiovisual theater and staff offices. Recreated second-floor spaces include a rotunda, legislative chambers, and smaller offices and meeting rooms. The building is located in the center of a large landscaped yard surrounded by a replica of the original 1850s ornamental iron fence.

The site offers tours, a short film, and occasional educational and recreational events.