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

John Elk, a Winnebago Indian, was born on an Indian reservation and later resided with whites on the non-reservation US territory in Omaha, Nebraska, where he renounced his former tribal allegiance and claimed citizenship by virtue of the Citizenship Clause.

The case came about after Elk tried to register to vote in 1880 and was denied by Charles Wilkins, the named defendant, who was registrar of voters of the Fifth ward of the City of Omaha.

Multiple ship owners sued because they were transporting Dutch immigrants, and the Netherlands had a treaty with the United States that they claimed prohibited the tax.

The decision established that treaties, which are described in the Supremacy Clause of the US Constitution as "the supreme law of the land" equal to any domestic federal law, do not hold a privileged position above other acts of Congress.