Earliest records indicate Edward J. Watson was chosen by the people to serve as the first City Marshal in 1872. Some of the duties of the early city marshals, included apprehending horse thieves and hauling hobos in and off the trains and rounding up the town drunks. Some of these offenders ended up in the calaboose (the first Jefferson County Jail is located in the Jefferson County Historical Village at 1411 N 27th Street, Mt. Vernon, Illinois.)

During the 1950's, the "Door Shakers" were organized. This group of merchant police were security guards hired by store owners to check and secure their businesses at night. Of course, they were always on the look out for break-ins and thieves. The exact dates of their disbursement isn't known. During this time parking meters were also installed downtown and are still in use today. A motorcycle patrol was added to the department in the 50's and in 2005, but is no longer in use today.

In May 1927, during Prohibition, the Mt. Vernon Police Department confiscated a load of alcohol in an undercover operations. Undercover operations still continue. In February 1995, the Mt. Vernon Narcotics Division working undercover conducted their first raid at a cocaine house and they seized cocaine, marijuana, firearms and guns.