The original, central section of the building was constructed in 1732 over the remains of Delaware's first court house (1689). In that same year, the building's cupola was designated as the center of a 12-mile radial circular boundary, creating Delaware's unique curved northern border. Additions and modifications were made to the building throughout the 18th and 19th centuries including the addition of the left and right wings.
Until the removal of the courts to Wilmington in 1881 as a result of the changing of the county seat, all jurisdictions of Delaware's courts, including federal court, had met, at one time or the other, in the New Castle Court House. In addition, the building served as Delaware's first state house and as the meeting place for Delaware's Colonial Assembly, and later, its first State Assembly.
In the court house's Assembly Room, legislators passed a resolution on June 15, 1776 separating from Great Britain and Pennsylvania, creating the Delaware State. Two months later on September 20, 1776, the first Constitution for the Delaware State was adopted. The building continued to serve as the state capitol until 1777 when governmental functions were transferred to Dover as a precaution against attack from British warships in the Delaware River.
Featured at the museum are exhibits on Delaware's colonial court and assembly, Delaware's Underground Railroad and abolitionists, and a special focus exhibit: "We the People....The Right of Trial by Jury."