The U.S. attorney in Chicago subpoenaed a fund-raising firm that had been co-owned by the daughter of Judge Juan Merchan, who conducted the trial that led to Donald Trump’s felony conviction.

The U.S. attorney’s office in Chicago has spent the past year investigating a Democratic fund-raising firm once co-owned by the daughter of the judge in President Trump’s hush-money trial in New York, according to court filings and people familiar with the inquiry.

Last August, the U.S. attorney, Andrew S. Boutros of the Northern District of Illinois, directed Authentic Campaigns Inc. to turn over a broad range of internal communications with clients. They included former Vice President Kamala Harris, former President Joseph R. Biden Jr., Gov. Kathy Hochul of New York, Representative Hakeem Jeffries of New York, and the Democratic National Committee, according to a grand jury subpoena reviewed by The New York Times.

Loren Merchan, the daughter of Juan Merchan, a supreme court judge in Manhattan, was the firm’s vice president until late 2024 and was also on the list. The Merchan family has been a frequent target of Mr. Trump and his allies, who have made unsubstantiated claims that the judge was out to get him and that his daughter profited from accusations aired at the trial.

The trial ended with Mr. Trump’s conviction in 2024, in the midst of his campaign for a second term, on 34 felony counts stemming from his efforts to keep a porn star from publicizing her story of a liaison with him.

The firm’s legal team, which included Preet Bharara, the former top federal prosecutor in Manhattan, sought to limit the request. Prosecutors eventually modified the subpoena, narrowing it to focus on a $468 payment from Ms. Harris’s presidential campaign, and emails between Ms. Merchan and her father, according to people with knowledge of the inquiry who requested anonymity to discuss an ongoing legal matter.

It is not clear where the investigation stands. No follow-up subpoenas have been issued to individuals, including Ms. Merchan, suggesting that prosecutors might not be actively working to charge anyone, those people added.