Long-serving Citizen reporter Sally Murrer was arrested along with a Thames Valley police officer, another from Herts Police, a soldier from Cambridge and a 52-year-old Hertfordshire man.
Police were investigating alleged leaks to the media and seized computers and paperwork from the Citizen office at Bletchley after spending several hours searching her desk.
Sally’s home was also searched and items taken away by police.
She was arrested on suspicion of aiding and abetting misconduct in a public office and was held in custody overnight before being released on bail.
The mother of three said: “I have had a lot of support from colleagues, fellow professionals and from the people of Milton Keynes with whom I have worked for more than 30 years as a reporter.
“I appreciate their trust and confidence in my integrity as a journalist.”
The Citizen’s parent company said in a statement: “Johnston Press will co-operate with the police inquiries but has no grounds to suppose that its reporter was not carrying out journalistic responsibilities fairly and legally.
“To support its reporter, the company will fund independent legal advice.”
The MK News’s office was also searched by police in connection with the investigation into alleged police leaks.
MK News co-operated with the police. No computers were seized and no reporter from MK News was arrested.
Steve Lowe, group editor of LSN Media, parent company of MK News, said: “The police visited our news office in Milton Keynes with a search warrant. We co-operated and will continue to do so if crimes have been committed.
“If, on the other hand, this is the police simply trying to spare its own blushes about leaks that may have been no more than embarrassing to them, we will take a dim view and pursue the matter.”