605 ILCS 5/5-107
Relocations of county highways may be made during the improvement thereof according to plans approved by the county board and the Department. Upon completion of the relocated highway and its opening to public travel, the new location shall become the location of the county highway and the county shall have full authority over the relocated highway and that portion of the original location not incorporated into the new location. For any portion of the original location not incorporated into the new location, the county board, by the process established by law, may transfer road jurisdiction to another highway authority or vacate, transfer, or sell the property interest.
Pending the completion and opening of the relocation, the county board shall have full authority over the existing county highway and shall also have power to lay out the relocation, acquire rights-of-way, by condemnation or otherwise, and take whatever action is necessary to effect the laying out, improving, and opening of the county highway upon the relocation.
605 ILCS 5/5-107