40 ILCS 5/5-217

Whenever any territory is annexed to the city, any person then employed as a policeman in the annexed territory who is employed by the city on the date of annexation as a policeman shall automatically come under the provisions of this Article and any term of service rendered by him in such territory shall be considered, for the purpose of this Article, as a term of service rendered in the city. Any such policeman shall in every respect, as of the date the annexation comes into effect, be considered a present employee of the city on the effective date.