65 ILCS 5/10-1-17
Officers who are elected by the people, or who are elected by the corporate authorities pursuant to the municipal charter, or whose appointment is subject to confirmation by the corporate authorities, judges of election, members of any board of education, the superintendent and teachers of schools, the employees of any welfare department, heads of any principal department of the municipality, the chief librarian of the public library, members of the law department, police officers above the grade of captain, police cadets, a health officer appointed after July 1, 1953, seasonal employees which means those persons whose employment does not exceed 90 days in any calendar year, one deputy and one private secretary of each of the elected municipal officials and the municipal manager, and administrative assistants to the mayor or municipal manager, shall not be included in such classified service, except that the chief of the police department may be included in the classified service if the corporate authorities so provides by ordinance.
Any position of employment in a public library that is operated under The Illinois Local Library Act and has an elected Board of Library Trustees may be excluded from the classified service by a 2/3 vote of the Board of Library Trustees.
65 ILCS 5/10-1-17