105 ILCS 5/11E-25

(a) Any contiguous and compact territory, no part of which is included within any unit district, may be organized into a unit district as provided in this Article. (b) The territory of one or more entire unit districts that are contiguous to each other, plus any contiguous and compact territory no part of which is included within any unit district, and the territory of which taken as a whole is compact may be organized into a unit district as provided in this Article.