Illinois wins boundary dispute — May 28, 1991 WASHINGTON — Illinois emerged a winner in the Supreme Court today in its longstanding boundary dispute with Kentucky over control of a section of the Ohio River.The court ruled unanimously that the boundary line between the two states is the river’s low-water mark as it existed in 1792. Illinois v. Kentucky, 106 Original.Kentucky had contended the boundary line should be the current low-water mark, subject to change with the Ohio’s shifting flow. Writing …