Four Chicago-area companies, including Oprah Winfrey’s production company, have notified the state they plan to cut a total of at least 250 jobs by July.Harpo Studios Inc., Ms. Winfrey’s company, filed a notice May 3 of a tentative plan to lay off an unspecified number of workers beginning May 25, according to the monthly Worker Adjustment and Retraining Notification Act report released Wednesday by the Illinois Department of Employment Security.

Ms. Winfrey ended her 25-year-old syndicated television show last month.

“Employees are being notified on a departmental basis whether their jobs will be eliminated,” a Harpo spokeswoman wrote in an e-mail. “Most of those leaving us are doing so voluntarily to pursue other interests.”

The spokeswoman declined to say how many jobs will be cut but acknowledged that it could be a third of the staff, which is the percentage that triggers a filing with the state.

“The process started on or about May 25 and is going on throughout the summer months,” she wrote. “We are tracking on a daily basis the number of employees who have accepted new positions or leave voluntarily vs. those who . . . suffer an ’employment loss’ within the meaning of the law. . . . All employees were made aware of this rightsizing months ago.”

As of December, Harpo had about 400 full- and part-time employees, after about 50 workers left last year to join the new Los Angeles-based Oprah Winfrey Network. In December, Harpo Co-president Erik Logan told Crain’s that he expected employees to remain at work after Ms. Winfrey’s show ended at the end of May. He said they would move to shows on the Oprah Winfrey Network.

Harpo told employees in March that former talk-show host Rosie O’Donnell would start taping a new, one-hour daytime show in Harpo studio space. The show will run on OWN. The state act, known as WARN, requires companies with at least 75 employees to give the state 60 days’ notice of closings or of making mass layoffs.