The Supreme Court rejected the reasoning behind the administration's proposed addition of the question, so the president would need to provide a new rationale.
The five conservatives on the court seemed ready to rule against three lower courts, a collection of researchers and experts, and five former leaders of the Census Bureau.
After a circuit court ordered the removal of a citizenship question from the census, the Trump administration asked the Supreme Court to weigh in on the case. On Friday, the high court agreed.
Uncertainty over the government's future operations and the addition of a citizenship question have left cities bracing for chaos during the upcoming census.
The judge ruled that, while the administration's move to include a citizenship question was not in itself unconstitutional, it was "unlawful for a multitude of independent reasons."