5 ILCS 70/1.20
"General superintendent of police," "secretary of the general superintendent of police," "assistant general superintendent of police," "first deputy superintendent of police," "chief of police," "assistant chief of police," "city marshal," "assistant city marshal," "deputy city marshal," "chief of detectives," "assistant chief of detectives," and all "captains," "lieutenants," "detective sergeants," "second-class sergeants," "sergeants," "inspector of police," "detectives," "patrolmen," "operators" and "civilian" or "plain clothes policemen" and "assistant identification inspector," mean "policemen employed and in the service of a municipality," and the term "police force," shall be construed to include such persons in the employ of a municipality as members of the department of police, who are or shall hereafter be appointed and sworn as policemen.
5 ILCS 70/1.20