Hastert, 68, a lobbyist and business consultant who left Congress in 2007, hired three former staff members at salaries of more than $100,000 apiece to run the publicly financed office, the Chicago Tribune inquiry found.
Taxpayers also pay Hastert's $6,300 monthly office rent, which goes to a company partly owned by three sons of a Hastert mentor and business partner, the newspaper said.
Other public funds pay for an $860-a-month 2008 GMC Yukon sport utility vehicle Hastert leased from a dealership owned by a friend and campaign donor, the newspaper said.
Hastert, who declined to talk with the Tribune, is taking advantage of a little-known perk given to former speakers, the Tribune said.
And he could have spent considerably more under the law if he had wanted, Hastert spokesman Brad Hahn told the newspaper.
He spent $1 million in two years, but could have spent nearly twice that, Hahn said.
Travel -- including airfare, hotels, taxis, tolls, gas, parking and mileage reimbursement for private vehicle use -- is also paid by taxpayers, the Tribune said.
One critic suggested Hastert could be bending the rules for use of public funds.
"When taxpayers give a million dollars, they intend specifically for the former speaker to wind down and finish his old job, and not for him to have a second career," University of Baltimore School of Law Professor Charles Tiefer, a former Democratic deputy general counsel of the House, told the newspaper.
Hahn said Hastert keeps his business ventures separate from the operation of his suburban Chicago office.