Retirement speculation has circulated since he forfeited the powerful speaker's post when Republicans lost control of the House in last year's elections. Hastert, 65, declined to run for minority leader, taking on a role as elder statesman among Republicans.
In his release, Hastert said his accomplishments as a congressman for his northern Illinois district and as House speaker weren't his own doing, but happened because of support from constituents, friends and colleagues.
"We worked together to pass legislation to provide a service or to meet the need or those we served," he said. "We fought for our beliefs and worked to improve our communities, our district and our country."
Hastert's retirement has local Democrats starting to boast they can win another congressional seat, even as the GOP vows it won't easily give up a seat it has held for two decades. Hastert was considered by many to be unbeatable in his northern Illinois district.
"Any Democrat thinking of getting into this race does so at his or her own peril," said National Republican Congressional Committee spokesman Ken Spain.
A Hastert vacancy is the second in Illinois that Republicans would have to contend with because retiring Rep. Ray LaHood is giving up a central Illinois congressional seat controlled by the GOP for nearly 90 years. LaHood will leave when his term ends in January 2009.
National Republicans "now have to defend another open seat in a blue state where the president is incredibly unpopular," said DCCC spokesman Doug Thornell.
Thornell said a race to replace Hastert would be a "a real opportunity" for Democrats in a "competitive district." The district stretches from Hastert's Plano home south of Chicago all the way to the Mississippi River.
Some local Democrats say they might snag Hastert's district away from Republicans because the populated areas are leaning more Democratic as people migrate there from the heavily Democratic city of Chicago in search of less expensive housing. They also point to last year's election, when two Democrats from Hastert's district won open seats in the Illinois Senate that had been held by Republicans.
"Times, they have a-changed," said state Sen. Michael Noland, one of those Democrats who now represents the Elgin area west of Chicago.
President Bush carried the district in 2004 with 55 percent of the vote.