There are often differences between a pilot film and the subsequent series. In this, Cannon has an assistant to help him, and his apartment has a maid, an exercise cycle, and an indoor shooting range. When the series started there was no assistant, maid, or exercise cycle but he still had a firing range, which was seen one time in an early season one episode. He lived in a different apartment in a different building.
J.D. Cannon, Murray Hamilton, Earl Holliman, Vera Miles, Lynne Marta, John Fiedler and Ross Hagen all appeared in the TV show "Rauchende Colts (1955)." William Conrad was the original Matt Dillon on the radio version of "Gunsmoke" & wanted the TV role but it was thought that he did not fit the role physically.
In the pilot of the series, Cannon drove a Lincoln Continental sedan (not a Mark III) . The car was wrecked by the bad guys in an attempt to scare Cannon off the case. Then, for most of the series, Cannon barreled around in a Lincoln Continental Mark IV(Mark III for the first season & a Mark IV for the remainder of the series). During the last part of the series' run, the chubby private eye's Cannonmobile was the Lincoln Continental Mark V(Not correct. The series ended in 1976. The Continental Mark V was introduced in 1977. The final year of the series was a 1976 Continental Mark IV)
Set in Gallitin and Warren Springs, in Coffey County, New Mexico (all fictitious).
Barry Sullivan and William Conrad had appeared together as police officers investigating a murder in the 1949 Noir film "Tension".