Thornhill, historic plantation in Greene County, Alabama, United States

Thornhill is a Greek Revival plantation house near Forkland, Alabama, built by 1833 and attributed to architect William Nichols. A two-story portico with six Ionic columns was added around 1850. The house is 55 feet wide, with a 14-by-40-foot central hall and spiral staircase; its eight rooms are 19.5 feet square, with 12-foot ceilings downstairs and 11-foot ceilings upstairs.

James Innes Thornton, born in 1800 in Virginia, moved to Alabama, practised law in Huntsville and served as Alabama's third secretary of state from 1824 to 1834 before retiring to Greene County. He developed Thornhill as a cotton plantation from the late 1820s, initially 2,600 acres and later over 5,000. The Greek Revival main house was completed by 1833, and the property was listed on the National Register of Historic Places on May 10, 1984.

The main house faces Greene County Road 20 near Forkland. The family cemetery lies a few hundred feet east of the house. The plantation schoolhouse, built around 1845, stands near the main house, surrounded by post oaks about 250 years old.

The main house was recorded by the Historic American Buildings Survey in 1934. Its two-story portico with six Ionic columns was added around 1850, attributed to builder David Rinehart Anthony of Eutaw, who also added the second-story balcony with crisscrossed lattice railing.