Latrobe's first major project in the United States was the State Penitentiary in Richmond, commissioned in 1797. The penitentiary included many innovative ideas in penal reform, then being espoused by Thomas Jefferson and various other figures, including cells arranged in a semicircle, that allowed for easy surveillance, as well as improved living conditions for sanitation and ventilation. He also pioneered the use of solitary confinement in the Richmond penitentiary. While in Virginia, Latrobe worked on the Green Spring mansion near Williamsburg, which had been built by Governor Sir William Berkeley in the seventeenth century but fell into disrepair after the American Revolutionary War. Latrobe created designs for Fort Nelson in Virginia in 1798. He also made drawings for a number of houses that were not built, including the "Mill Hill" plantation house near Richmond.