Republicans get to add another red seat to Congress.
Roughly 300 votes separated the two candidates.
In a statement, Walsh congratulated Bean on the "vigorous" campaign and thanked her for her six years of public service.
"We can turn all of our energies to advancing the legislative agenda the people of the 8th District have told me to pursue: more responsive government, less borrowing against our children's future, and a common sense approach to deal with the economic challenges facing our country," he said, adding that he'll be back in Illinois soon to "personally thank all those who worked to hard to send me to Congress."
Walsh was a Tea Party favorite, and a group from Palatine called his victory "the upset of 2010."
"This is a huge win for all the grassroot organizations that supported Walsh," the Palatine Tea Party said in a release. "Against all odds we defeated incumbent Melissa Bean (D) who had significantly more money and media support."
Bean has held the seat since 2004 when she defeated Republican Rep. Phil Crane. Walsh's victory means the state's 19-member congressional delegation will have 11 Republicans, contributing to the state's first GOP majority for Illinois in seven years.
In Lake County, Walsh had 55,148 votes compared with Bean's 52,026, according to updated results on Lake County's clerk
website. In McHenry County, Walsh had 19,119 compared with Bean's 15,774, according to the clerk on Tuesday evening. In Cook County, Walsh had 23,848 votes compared with Bean's 30,025, according to Cook County Board of Elections spokeswoman Courtney Greve.
Election authorities in those counties have a Nov. 23 deadline to certify results with the Illinois State Board of Elections.
Both Walsh and Bean headed to Washington this week. Bean was there to finish up work in the lame duck sesssion of Congress, while Walsh went for freshman orientation.
Walsh has never held public office but has tried before: He ran unsuccessfully for Congress in 1996 and for the Illinois House in
Bean was back in Illinois on Tuesday night and has scheduled a Wednesday press conference to provide more formal remarks.