The Duke of Sussex, 40, moved to California in 2020 with his wife Meghan, 44, after stepping back from royal duties.
His immigration status in the US has been under question since he admitted in his memoir Spare to using cocaine and marijuana.
The disclosures in legal filings show that 1007 papers concerning Harry were identified within the Department of State, which oversees visa applications.
According to the records, 217 documents are held by the Office of the Secretary of State, while 517 "potentially responsive records" were found within the Bureau of Consular Affairs.
A further 271 papers are held by the Office of the Legal Adviser and two by the Office of the Deputy Secretary of State.
The documents are now due to be reviewed by a federal judge in Washington to decide what, if any, may be released publicly.
The development follows a lawsuit filed in January by the Heritage Foundation, a rightwing think-tank, which had previously sued the Department of Homeland Security in a bid to access Harry's immigration records.
While the action led to the release of several files, none disclosed details of his visa status or whether he provided accurate information in his application.
Heritage has claimed in its latest filing that Harry may have withheld details of his past drug use despite writing in Spare that he had taken cocaine and smoked marijuana.
The organisation's lawyer Samuel Dewey said the scale of documents located was significant.
"The number of papers on Harry shows they are monitoring him pretty closely. I think we're going to see documents from Harry talking about the case, but other material may be withheld. Then it will be up to politicians whether that decision is overruled," he said.
The lawsuits have prompted speculation about how the Trump administration might respond to Harry's residency in the US.
Trump has previously been critical of Harry and Meghan.
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