Thornhill is an old plantation house near Forkland, Alabama. The Greek Revival main house was built in 1833 by James Innes Thornton. Thornhill was a cotton plantation in the early 1830s. It extended over 2,600 acres. By 1860, there were 156 slaves working on the plantation. About a third of the slaves lived in quarters behind the main house. William Nichols is believed to be the architect. The house measures 55 feet wide. Inside is a 14 ft wide by 40 ft long central hall. There is a spiral staircase at the back. There are two rooms to either side. The left front room was the parlor. The dining room was behind it. On the front right was the master bedroom. The plantation office was behind it. Upstairs is a matching hall and four bedrooms. All eight rooms are 19.5 feet square. The downstairs rooms have 12-foot ceilings. The upstairs ceilings are 11 feet. There was once a brick kitchen behind the house. It later burned. Additions were made to the original house from 1890 to 1949. They were razed in 1994 and rebuilt to better match the original intent. The two-story portico with six Ionic columns was added about 1850. The plantation schoolhouse was constructed about 1845. The Thornton children and neighboring plantation children were taught there. Surrounding the schoolhouse are 230-year-old post oaks. The house was placed on the National Register of Historic Places on May 10, 1984.