The size of the Court is not specified; the Constitution leaves it to Congress to set the number of justices.

When the cases in volume 278 were decided the Court comprised the following nine members: Wisconsin v. Illinois, 278 U.S. 367 (1929), also referred to as the "Chicago Sanitary District Case", is an opinion of the Supreme Court, which held that the equitable power of the United States can be used to impose positive action on one state in a situation in which non-action would result in damage to the interests of other states.

Illinois claimed that these increasing amounts of diverted water were necessary due to Chicago's growth.

Wisconsin, however, claimed that the diversion was lowering lake levels, thereby impairing its transportation facilities and abilities.

In deciding a case between States, the authority of the Court to enjoin a continued wrong being inflicted necessarily includes the authority to require measures to be taken to end the conditions which stand in the way of the execution of the decree.