Thomas W. Cahill (December 25, 1864 — September 29, 1951) was one of the founding fathers of soccer in the United States, and is considered the most important administrator in U.S. Soccer before World War II. Cahill formed the United States Football Association in 1913, which would later become the United States Soccer Federation. In 1916 he became the first coach of the United States men's national soccer team. Cahill was enshrined in the U.S. National Soccer Hall of Fame in 1950.
Thomas Cahill was born in New York City, but moved to St. Louis, Missouri in 1871. He was of Irish descent. He attended St. Louis University and built a reputation as one of the pre-eminent amateur athletes in the country. Originally favoring running and baseball, he became interested in soccer after witnessing a game involving a team visiting from Toronto.
In 1897, Cahill founded St. Louis Shamrocks which competed in the St. Louis Association Foot Ball League. They won the league title in 1899 and 1900. Although he owned Shamrocks, he also managed several other team including St. Louis Spalding's in 1903-04 and Diel F.C. during the 1904-05 season.
Cahill returned to the East Coast and settled in Newark, New Jersey in 1910.
Cahill decided to establish a national governing body for soccer. He was the secretary and one of the founders of the American Amateur Football Association, one of the governing bodies vying for sole status as the nationally recognized governing body. He traveled to in 1912 to attend FIFA's ninth annual congress where he applied for the American Amateur Football Association, to become the U.S. national governing body. Cahill's efforts were opposed by a representative from the American Football Association, a rival also attempting to become the nationally recognized body. FIFA did not immediately resolve the dispute, and urged Cahill and the AAFA to work with the AFA to create a solution.