In the case of Iowa v. Illinois in 1892, the U.S Supreme Court was asked to settle a dispute over the boundary line between these two states. The disagreement arose from differing interpretations of an 1839 survey that had been conducted to establish this border along the Mississippi River. While both states agreed that their shared border ran down the middle of this river's main channel, they disagreed on where exactly this main channel lay due to changes in its course over time caused by natural forces and human intervention. In its decision, the court ruled in favor of Illinois' interpretation based on historical usage and possession since it was more consistent with international law principles for determining territorial boundaries when rivers change their courses naturally or artificially over time.

The dissenting opinion in the case of Iowa v. Illinois (1892) argued that the majority's decision to establish a boundary line between Iowa and Illinois along the middle of the main channel of navigation on Mississippi River was incorrect. The dissenters believed that this ruling contradicted previous decisions made by Congress, which had established state boundaries at low-water mark on one side or another depending upon whether it was an eastern or western river. They also pointed out inconsistencies with international law principles regarding boundary disputes over navigable rivers, which typically place boundaries at thalweg - deepest part of a river - rather than mid-channel. Furthermore, they contended that historical practice and understanding supported their interpretation as well as practical considerations such as avoiding potential conflicts over jurisdiction and control over islands in the river.