The most conspicuous structure of the town square is the handsome courthouse with its projecting portico carried on great brownstone columns, one of which bears scars of a Confederate shell fired during the occupation of the town in the days leading up to the battle of Gettysburg. It is one of the first Pennsylvania county buildings to break with the broader proportions of the Greek Revival and return to Rome's more vertical proportions. The cupola and pediment, now painted white, were once dark brown like the columns, better unifying the principal elements of the facade. It is the work of local architect Samuel Bryan Jr., who is credited with the similar courthouse in Greene County's Waynesburg. A variety of additions at the rear have only modestly affected the composition, while the interior is one of the better preserved, retaining much of its midcentury character with an overlay from the late nineteenth century.

Modern government now encompasses a much larger sphere necessitating a new courthouse, across Hanover Street on the site of the town's great 1870s market. It is further evidence of the mania for things colonial that has captivated Carlisle's old elite. Lawrie and Greene, who designed the interesting Moderne Dauphin County Courthouse (DA9), produced this Williamsburg-derived brick and limestone porticoed hulk.