The Lawrence County Courthouse, one of eight pre–Civil War Greek Revival courthouses in western Pennsylvania, looks to the west over the town of New Castle from its hillside site. Dominated by a pedimented portico supported by six Ionic columns, the brick gable-roofed building is painted a cream color. The source of the design is Thomas Jefferson's State Capitol in Richmond, Virginia. The contractors, William Hamilton and James Craig, hired a free African American, P. Ross Berry, as the chief mason. An addition in 1888 of four bays south of the five original bays uses the same vocabulary of dentiled cornice and fascia, but with shrunken Ionic columns at the recessed porch and pilaster strips delineating the bays. Several glass and concrete–paneled additions over the years have compromised the courthouse's integrity, although its cupola has been restored. In 1979, a three-story hexagonal wing with recessed ribbon windows and a hipped roof was attached to the older building by a glass hallway at the southeast corner.