NPR and Snopes have explained that the decennial census hasn't included a nationwide citizenship question on the census since 1960. In 1970, the citizenship question moved to a long-form questionnaire sent to fewer than 20% of American households. In 2010, the long-form questionnaire was replaced by the annual American Community Survey, which includes a citizenship question.
From the July 8 edition of Fox News' Fox & Friends:
PETE HEGSETH (GUEST CO-HOST): Why did the Supreme Court step in -- if there's constitutional rationale, why are they stepping in and creating confusion here?
JENNA ELLIS RIVES (ATTORNEY): It's a ridiculous act of political activism, because the Constitution clearly leaves the process up to Congress, which since 1790, has provided implementing legislation to carry out the census. There have been other executive orders. And the executive branch is required to enforce the census and count the people so that we know that we can participate in the franchise and have free and fair elections. It's just common sense to count the citizens in the states. So what the Supreme Court has done, has said, is that the citizenship question -- which by the way has been on every census since the early 1800s, it was simply removed by the Obama administration in 2010. This is a reinstatement, that the question doesn't violate either the Enumerations Clause in the Constitution or Congress' legislation. They're simply requiring President Trump to provide further rationale.