Alonzo Jay Edgerton(June 7, 1827 - August 9, 1896) was an American politican. He was appointed US Senator from Minnesota as a Republican, and served from March 12, 1881 to October 30, 1881. He was later appointed chief justice of the Territorial Supreme Court of Dakota. When South Dakota was admitted as a State into the Union, he was made United States judge of that district. He also served as president of the constitutional convention of South Dakota. He died in Sioux Falls, South Dakota.