Frank S. Cahill (27 January 1876, in Calumet Island, Quebec – 17 April 1934), was a politician, broker, clerk and real estate broker. The son of William Cahill, he was educated in Campbell's Bay, Quebec. Cahill worked as a postal clerk in Sault Ste. Marie, Michigan for several years, then moved to Saskatchewan, working as a real estate broker in Saskatoon. In 1909, he opened another real estate office in Ottawa. Cahill married Mildred Coyne in 1910.