The form showed Walker received payment of more than $1,000 from his publisher for "Unintimidated: A Governor's Story and a Nation's Challenge," which was released in November. Walker co-wrote the book with Marc Thiessen, a former speechwriter for President George W. Bush.
Walker's book further fueled speculation that the first-term Republican governor is positioning himself for a 2016 presidential run. Walker faces re-election in November; he'll be challenged by likely Democratic nominee Mary Burke, a former state commerce secretary and Trek Bicycle Corp. executive. Burke is required to file her statement of economic interest by June 5.
Walker has declined to say how much he was paid for the book, which detailed his high-profile 2011 fight with public unions and the subsequent recall election. Penguin Group imprint Sentinel, the book's publisher, has also declined to say how much Walker was paid.
As of Sunday, the book had sold 18,000 copies in six months, according to Nielsen. Its numbers account for about 85 percent of the print book market. Nielsen does not track any e-book sales.
Walker's non-disclosure drew criticism Wednesday from his political foes, who have also called on Walker to disclose who donated to his legal defense fund that was first established to deal with a criminal investigation into his former aides and associates.
"This report shows Gov. Walker continues to keep secret from the people of Wisconsin both the details of how much he personally enriched himself for his lucrative pre-presidential campaign book deal, as well as who financed his criminal defense fund," said Scot Ross, director of the liberal advocacy group One Wisconsin Now. "Given the corruption, cronyism and incompetence surrounding his administration, the people deserve much more information than what Gov. Walker has shielded from public scrutiny."
Walker's campaign spokesman referred questions to his official office. A spokeswoman did not immediately return a message.
Office holders, candidates and others in state government must list on the form that Walker filed investments, income, business activities, real estate, creditors and other financial information. However, the form requires filers only to check the value of investments as being either between $5,000 and $50,000 or above $50,000.
Walker reported having two mutual funds each worth between $5,000 and $50,000, in addition to similar investment ranges in a pair of state retirement funds.
Walker reported owing more than $50,000 to both Bank of America and Green Tree, a home loan company based in South Dakota. Walker and his wife, Tonette, own a home in Wauwatosa and also have two sons in college.
Walker's book payment was the only additional source of income he listed outside of his employment as governor and his wife's job at the American Lung Association.
He also voluntarily reported receiving 46 gifts last year worth more than $50, including an Aaron Rodgers jersey and signed picture from his staff, two bottles of Reagan Ranch olive oil from the Young America's Foundation Reagan Ranch Center and six bottles of wine from the Door Peninsula Winery in Sturgeon Bay.
All of the items were disposed of consistent with state law and guidance from the state Government Accountability Board, Walker's report said. That guidance includes giving the items to other state agencies or institutions that can use them, donating them to charity, returning the item to the giver or purchasing the item outright.