Isaac Herschel Goodnight (January 31, 1849 – July 24, 1901) was a United States representative from Kentucky.

Isaac Goodnight was born near Scottsville, Kentucky on January 31, 1849.^[1] He was the son of Isaac and Lucinda (Billingsby) Goodnight.^[2] He is the great nephew of Isaac Goodnight of Harrodsburg, Kentucky, born January 1, 1782, who is believed to have been the first white male child born in what is now Kentucky.^[2]

Goodnight attended the common schools of the area.^[1] In 1870, his family moved to Franklin, Kentucky.^[2] He matriculated to Cumberland University in Lebanon, Tennessee earning a degree in 1872 a law degree in 1873.^[2] He returned to Franklin, serving as deputy circuit clerk while reading law, and was admitted to the bar in 1874.^[2] He commenced practice in Franklin.^[1]

On March 12, 1879, Goodnight married Ella Hoy.^[3] The couple had one son, Hoy Goodnight.^[3]

In 1877, Goodnight was elected to the Kentucky House of Representatives, serving a single, two-year term.^[2] He served as the chairman of the Democratic Kentucky convention at Louisville, Kentucky in 1891.^[1] He was elected to represent the Third District in the U.S. House of Representatives in 1888.^[2] He was twice re-elected, serving in the Fifty-first, Fifty-second, and Fifty-third Congresses (March 4, 1889 – March 3, 1895).^[1] During his tenure, he was a member of the Judiciary Committee, rising to third in seniority on that committee by the end of his third term.^[2]

Due to ill health and the fact that his absence from home was hurting his legal practice, Goodnight did not seek re-election in 1894.^[2] After leaving Congress, he was elected a judge of the seventh Kentucky circuit in 1897 and served until his death in Franklin on July 24, 1901.^[1] He was buried in Green Lawn Cemetery.^[1]

His home in Franklin, the Goodnight House, is listed on the National Register of Historic Places.