605 ILCS 5/10-201
Bridges across streams forming the boundary line between this and any adjoining state, or bridges upon any road which lies upon the boundary line between this and any adjoining state, may be constructed or repaired by any county or counties of this State contiguous to the proposed construction or repair, acting in conjunction with any county, municipality or subordinate division of the adjoining state, as provided in this Division of this Article. A bridge may likewise be constructed at the point of intersection of any highway with the boundary line between this and any adjoining state, or a bridge already constructed at such point may likewise be repaired, as provided in this Division of this Article. A county shall be deemed contiguous to such construction or repair if any part of such county lies within 80 rods thereof. The total of the cost to be borne by any county (or counties) of this State shall not exceed one-half of the total cost of such construction or repair.
605 ILCS 5/10-201