Alfred Delavan Thomas (August 11, 1837 – August 8, 1896) was a United States federal judge.
Born in Delavan, Wisconsin, Thomas read law and graduated from Brown University in 1861. He was a district attorney of Walworth County, Wisconsin, from about 1861 to 1867, and had a private practice in Delavan from 1864 to 1877, and in Fargo, North Dakota beginning in 1878. He was attorney to the Homestake Mining Company of Deadwood, South Dakota until 1882, returning to private practice in Fargo from 1882 to 1890.
On February 19, 1890, Thomas was nominated by President Benjamin Harrison to a new seat on the United States District Court for the District of North Dakota created by 26 Stat. 67. He was confirmed by the United States Senate on February 25, 1890, and received his commission the same day. He served in that capacity until his death, in Fargo.