John Fletcher Darby (December 10, 1803 – May 11, 1882) was a U.S. Representative from Missouri and the fourth mayor of St. Louis.

Darby was born in Person County, North Carolina.

He was the Mayor of St. Louis from 1835 to 1837 and 1840 to 1841, between which he served as a member of the Missouri Senate, in 1838.

During his time as mayor, Darby was very active in getting the first Missouri railroad convention held in St. Louis.

He died near Pendleton, Missouri, on May 11, 1882, and his remains are interred at Calvary Cemetery in St. Louis.