This series set a new record for the longest run of any Australian series without a single change of cast, at 226 episodes. That record remains unbroken.
Throughout the series' run, the regular male characters are credited on-screen by their surnames only (Banner, Vickers, Dwyer, MacLeod and Peters).
The series was originally intended to be set in St Kilda, with some of the sets constructed at the GTV9 studios in Richmond (where some corridors and doorways were added specifically for the series) being replicas of the charge counter and Criminal Investigation Branch (CIB) room at the St Kilda police station, with the attention to detail extending to having the same picture on the wall. When the St Kilda City Council objected to the series in November 1968 and claimed that it would do great harm to the property values and image of the suburb, the series concept was changed and it was set in the fictitious suburb of Yarra Central. Ian Jones was disappointed that the original concept wasn't followed through because he felt that if it had, the series would have been further based in reality and would have had a cosmopolitan ambience that couldn't be found in a fictitious location.
95 Montague Street South Melbourne was the fictitious Yarra Central police station building location. The building has since been demolished and a modern building put up in its place. A police station plaque was put up on the wall at the front entrance during filming of some episodes. The closing titles of later episodes featured a slow zoom in from the building to this plaque.
Among the early titles considered for the series were "Saints and Sinners", which would have been appropriate for the St. Kilda setting of its early development, and "Police File", a title first used after the concept was changed, which Crawford Productions weren't happy with. In their search for another name, one of the titles suggested was "Department 24", a throwback to the successful Crawfords radio serial "D24", which had evolved into the television series Homicide (1964). A secretary preparing a list from the suggestions mistyped "Department 24" as "Division 4", a title that struck a chord when the list was presented, and was subsequently adopted as the title for the new series.