Keyran William Jack "Bill" Cahill (3 December 1911 – 7 March 1966) was a sportsman who played Australian rules football for Essendon in the Victorian Football League (VFL) during the 1930s and represented Tasmania at first-class cricket.
Cahill, a half back, won two Tasman Shields Trophies while at Northern Tasmanian Football Association club Launceston, in 1933 and 1936.
He struggled in his two seasons at Essendon due to a shoulder injury and returned to Launceston in 1939 where he was appointed captain-coach.
He had earlier made four first-class appearances with Tasmania in the 1931/32 season.
One of those was against the touring South African team and he took the only wicket of his career when he dismissed all-rounder Quintin McMillan.