The tour officially adopted the name PGA Tour in 1975.
The organization was originally called the Tournament Players Division, created within the Professional Golfers’ Association of America. In December 1968, touring professionals separated from the PGA of America and formed an independent organization focused on tournament players rather than club professionals.
The 1975 name change helped establish “PGA Tour” as the public identity of the professional circuit. It is easy to confuse this date with 1968, which marks the tour players’ organizational break from the PGA of America, or with 1981, when the circuit briefly used another name during a dispute.
The PGA Tour name was not permanent in every year: in late August 1981, the organization changed its name to the TPA Tour. The dispute was settled within seven months, and the PGA Tour name returned in March 1982. Thus, 1975 is the canonical answer for when the tour officially adopted the PGA Tour name.