The U.S. Supreme Court case Illinois v. Missouri in 1969 revolved around a dispute between the two states over their shared boundary along the Mississippi River, specifically at its confluence with the Des Moines River. The controversy arose due to changes in the course of these rivers over time, which led to uncertainty about where exactly the state line was located. Illinois claimed that it owned certain islands and territory on what is now considered as Missouri's side of river based on historical boundaries while Missouri argued that shifts in river channels had moved those areas into its jurisdictional control. The Supreme Court appointed a Special Master to investigate and make recommendations regarding this border dispute. After extensive research including review of historical documents and physical surveys, he recommended that court should rule largely in favor of Missouri’s claims because natural changes (accretion) rather than sudden shifts (avulsion) had caused most alterations to river courses. In accepting his findings, Justice Potter Stewart wrote for unanimous court stating "the boundary is not an unchanging imaginary line but moves with gradual accretions or losses occasioned by action" of rivers involved.

In the dissenting opinion for Illinois v. Missouri, 1969, it was argued that the majority's decision to dismiss Illinois' complaint against Missouri on grounds of lack of jurisdiction was incorrect. The dissenters believed that the Supreme Court did have original and exclusive jurisdiction over disputes between states under Article III, Section 2 of the Constitution. They contended that this case involved a controversy between two states regarding their respective rights and obligations under an interstate compact approved by Congress - which is exactly what falls within the purview of Supreme Court’s original jurisdiction as per them. Furthermore, they disagreed with majority’s view about not having power to enforce terms of such compacts or agreements among states; instead they held a belief in court's ability to interpret and apply these compacts just like any other federal law.