Edward Prentiss Costigan (July 1, 1874January 17, 1939) was a Democratic Party politician who represented Colorado in the United States Senate from 1931 to 1937. He was a founding member of the Progressive Party in Colorado in 1912. Early life and education Edward Prentiss Costigan was born near Beulahville in King William County, Virginia, on July 1, 1874. His parents were George and Emilie (Sigur) Costigan. In 1877, his parents moved to Lake City, Colorado, and the following year settled in Ouray. After five years in Ouray, his father was appointed judge of the newly-formed San Miguel County, Colorado, by Governor James Benton Grant. He was elected the judge of Telluride two times. Both of his parents had an interest in mining and were owners of the Belmont mine and in mining in Mono County, California. The family resided in Denver, where his mother was a prominent member of the Denver Women's Club. Costigan attended Denver public schools, including East Denver High School. He studied law and was admitted to the bar in Salt Lake City in 1897. He graduated from Harvard University in 1899. His brother, George Purcell Costigan, Jr. was a lawyer, professor, dean, and author. Career The following year, he moved to Denver, Colorado, and practiced law. In 1902, he was declared the winner in the election as state representative, but a contest prevented his assuming his seat at the House of Representatives during the session. He began a fight for honest elections, which lasted over a decade. In 1906, he became a lawyer for the Honest Election League as well as the Law Enforcement League, the latter position he held for two years. He fought for a local option law as legal advisor, which was sustained in the Colorado Supreme Court. Costigan was chairman of the Dry Denver Committee in 1910 and was the president of the Civil Service Reform Association of Denver. During this period, he ran his law practice. He litigated freight rate cases before the Interstate Commerce Commission, representing Arizona commercial organizations and the Denver Chamber of Commerce. He was an attorney for the United Mine Workers of America in 1914 during a congressional investigation into the Colorado coal strike. There were several murder cases that occurred during the strike and Costigan secured acquittals for a number of defendants. Initially a Republican, in 1912 he was a founding member of the Progressive Party