Alonzo Barton Cornell (22 January 1832–15 October 1904) was born in Ithaca in Tompkins County, New York. He was the eldest son of Ezra Cornell, the founder of Cornell University. He was educated at the Ithaca Academy, and a the age of fifteen began a career in the field of telegraphy, later serving as a manager in telegraph offices. Afterwards, he owned steamboats on Cayuga Lake and was a bank official.

He was married to Elen Agusta Cornell.

He was an official of the Western Union Telegraph Company, founded by his father from 1868 to 1876. He was a surveyor of customs in New York City, chairman of the state Republican Party, and Speaker of the state assembly in 1873.

Cornell was Governor of New York from 1880 to 1882. He wrote a biography of his father in 1884. He established the state board of health and railroad commission.

Although he lived in New York City during his latter years, Cornell died in Ithaca, New York.