The U.S. Supreme Court case Iowa v. Illinois in 1893 was a dispute over the boundary line between the two states, specifically regarding the Mississippi River's mid-channel as their common border. The controversy arose when islands formed due to changes in the river's course, leading to confusion about which state had jurisdiction over them. The court ruled that despite shifts in its channel, the middle of main navigable channel of Mississippi at time it became a boundary remains constant and is considered as boundary line for both states regardless of any subsequent geographical alterations caused by natural forces or human intervention. Therefore, islands forming on one side or another did not alter this established border.

In the dissenting opinion for Iowa v. Illinois, it was argued that the boundary line between Iowa and Illinois should not be determined by a 1785 ordinance but rather by natural landmarks such as rivers. The justice believed that using an artificial construct like an ordinance to determine boundaries could lead to confusion and disputes in the future. He also pointed out inconsistencies in how different states interpreted this same ordinance, leading him to conclude that relying on it would only perpetuate these discrepancies further. Furthermore, he felt there were issues with fairness since some states might benefit more than others from its application due to geographical advantages or disadvantages. Therefore, he advocated for a more equitable approach based on physical geography instead of legal constructs.