65 ILCS 5/10-1-13
The commission shall, by its rules, provide for promotions in such classified service, on the basis of ascertained merit and seniority in service and examination and shall provide, in all cases where it is practicable, that vacancies shall be filled by promotion. All examinations for promotion shall be competitive among such members of the next lower rank as desire to submit themselves to such examination and the results thereof and the promotional eligible registers prepared therefrom shall be published by the commission within 60 days after any examinations are held. If two or more applicants achieve the identical final grade average, they shall be placed on the promotional eligible register in their order of seniority in the position from which they seek promotion. The commission shall submit to the appointing power the names of not more than 3 applicants for each promotion having the highest rating except that a commission in any municipality with more than 130,000 but less than 2,000,000 population may submit the names of not more than 5 applicants having the highest rating for each promotion, but in making his selection the appointing authority shall not pass over the person having the highest rating on the original register more than once and shall not pass over the person having the second highest rating in the original register more than twice. The commission shall strike off all names of applicants from a promotional eligible register after they have remained thereon no less than 2 years and no more than 3 years, provided that the commission shall notify the appointing power before the names are stricken and such appointing power shall fill any existing vacancies before all names are stricken from the promotional eligible register. The method of examination and the rules governing the same, and the method of certifying, shall be the same as provided for applicants for original appointment.
This amendatory Act of 1971 does not apply to any municipality which is a home rule unit.
65 ILCS 5/10-1-13