An episode featuring a Chicago cop taking a bribe led to Mayor Richard J. Daley banning any television show or film from doing any shooting in Chicago at all. That ban was later broken with the filming of The Blues Brothers (1980).
The show was inspired by the exploits of legendary Chicago crime fighter Detective Superintendent Joseph Morris. Detective Lieutenant Frank Pape, who worked for Morris, served as a Technical Advisor on the show, without getting credit, however, because of his active status within the Chicago Police Department, which banned police moonlighting.
The format and style of this series provided the inspiration for the spoof cop comedy 'Police Squad' (1982) and the feature film 'The Naked Gun' (1988) and it's sequels.
The theme music was provided by legendary jazz pianist Count Basie.
The album, "The Music from M Squad" (RCA Victor LPM-2062 and LSP-2062) was released in 1959. Over 40 years later, it was reissued on CD.