Jonathan Harrington Green (c. 1813–1887) was an American gambler, inventor, writer and later reformer in New York City during the early-to mid 19th century.
After living in Texas for several years, he joined a Methodist Episcopal church and suddenly abandoned gambling in 1842.
His popularity as "the Reformed Gambler" gained a significant following and helped pass anti-gambling laws in several states.
On February 20, 1851, he presented his findings at the Brooklyn Tabernacle reporting the existence of an estimated 6,000 gambling houses, 200 of these being high-class establishments "catering to men of standing and sound financial substance", as well as several thousand raffling, lottery and policy houses.
Green returned to Indiana at the start of the American Civil War and became a captain in the Union Army and was later employed by the US Secret Service.