105 ILCS 5/3-1.1
Whenever a unit school district is located in more than one educational service region, a qualified elector residing in that unit school district but outside of the educational service region administered by the regional superintendent of schools having supervision and control over that unit school district shall be eligible to vote in any election held to elect the regional superintendent of schools of the educational service region that is administered by the regional superintendent of schools who has supervision and control over that unit school district, but the elector shall not also be eligible to vote in the election held to elect the regional superintendent of schools of the educational service region in which the elector resides.
Not less than 100 days before each general primary election, the regional superintendent of schools shall certify to the State Board of Elections a list of each unit school district under his or her supervision and control and each county in which all or any part of each of those districts is located. The State Board of Elections shall certify each of those unit school districts and counties to the appropriate election authorities within 20 days after receiving the list certified by the regional superintendent of schools.
The election authority in a single county educational service region whose regional superintendent of schools exercises supervision and control over a unit school district that is located in that single county educational service region and in one or more other educational service regions shall certify to the election authority of each of those other educational service regions in which the unit school district is located the candidates for the office of the regional superintendent of schools exercising supervision and control over that unit school district.
105 ILCS 5/3-1.1