Background
Edward Prentiss Costigan was born on July 1, 1874 near Beulahville, King William County, Virginia, United States. He was the second in a family of two sons (a third died in infancy) of George Purcell and Emilie (Sigur) Costigan. He was of Dutch-Irish descent through his father and Spanish through his mother. Both parents had been born and brought up in Ohio, in or near Cincinnati, moving after their marriage to Chicago. Because of Mrs. Costigan's health they sought a better climate, first in Virginia and then in the recently opened San Juan country in southwestern Colorado, to which they moved about 1877. There the father practised law, served as a county judge, and engaged in mining ventures. Both Edward and his older brother, George Purcell Costigan, later a distinguished teacher of law, followed their father's legal bent.