The Rock Island Bridge case was a landmark decision by the United States Supreme Court in 1867. The case involved a dispute between the states of Illinois and Iowa over the construction of a bridge across the Mississippi River. The bridge was to be built by the Rock Island Railroad Company, and the states disagreed over the right of the company to build the bridge. The Supreme Court ultimately ruled in favor of the Rock Island Railroad Company, finding that the company had the right to build the bridge. The Court held that the states had no authority to interfere with the construction of the bridge, as it was a matter of interstate commerce. The Court also held that the states could not impose taxes or other restrictions on the bridge, as this would be a violation of the Commerce Clause of the Constitution. The decision in the Rock Island Bridge case was a major victory for the railroad industry, as it established the principle that states could not interfere with interstate commerce. The decision also established the principle that the federal government had the power to regulate interstate commerce, and that states could not impose taxes or other restrictions on interstate commerce. The decision was an important step in the development of the modern American economy.

In The Rock Island Bridge case, the Supreme Court was tasked with determining whether or not a bridge built by the United States over navigable waters of the Mississippi River constituted an obstruction to navigation. The majority opinion held that it did and thus violated federal law. However, in his dissenting opinion Justice Grier argued that Congress had granted permission for such bridges to be constructed and therefore this particular bridge should not be considered an obstruction. He further noted that if Congress had intended for all bridges over navigable waters to constitute obstructions they would have made their intentions clear in legislation rather than leaving it up to interpretation by courts. Ultimately he concluded that since there were no laws explicitly prohibiting such construction then this particular bridge should remain standing as its presence does not impede navigation on the river any more than other objects already present do so.