The Democratic front-runners former state Rep. Robin Kelly, former U.S. Rep. Debbie Halvorson and Chicago Alderman Anthony Beale made Election Day stops at train stations and restaurants in the district that spans Chicago's South Side, south suburbs and some rural areas.
They were among 14 Democrats and four Republicans in the special primary, but the Democratic winner was expected to sail through the April 9 general election because of the area is heavily Democratic.
Halvorson, who lost a primary challenge to Jackson last year, has been targeted by opponents for her position on gun control, which became a key issue in the district, parts of which have been deeply affected by Chicago's gun violence.
Independence USA, the super PAC of New York City Mayor Michael Bloomberg, poured more than $2 million into the race for anti-gun ads in support of Kelly and against Halvorson, a former state lawmaker and one-term congresswoman. Kelly supports an assault-weapons ban, but Halvorson does not.
After casting her ballot, Halvorson warned that if the ads are successful Bloomberg will try to "buy seats" across the country.
"We can't let that happen," she said.
Beale also took issue with the ads, saying people are "extremely upset" that someone from New York is trying to tell people in Illinois how to vote and predicting that there will be a "backlash."
The guns issue dominated candidate forums and television ads and also appeared to have resonated with voters.
Mary Jo Higgins of south suburban Steger said she voted for Halvorson because the former congresswoman is "the only Democrat who believes in the Second Amendment."
But Country Club Hills minister Rosemary Gage voted for former state Rep. Robin Kelly because Kelly is "standing with (President Barack Obama) and trying to get rid of guns."
"It's really bad in Chicago and across the country," Gage said. "Too many children have died."
The issue of ethics was also on the minds of voters, particularly as Jackson's legal saga has been playing out in federal court. He pleaded guilty early this month to charges that he misspent $750,000 in campaign money on lavish personal items, including a Rolex watch and furs. His departure created a rare opening in the district.
Halvorson was greeted by cheers of "good luck" and "go Debbie go" as she cast her ballot at a suburban community center in the village of Steger.
Speaking afterward, she said it's time for voters to close the chapter on Jackson's ethical problems and send someone to Washington who can hit the ground running.
Halvorson is counting on voters in the southern, more rural part of the district, where she grew up, to help her to a win in the primary.
David Berchem, a retired painter, said he voted for Halvorson because he believes she will represent all residents of the district and she's "as honest a person as you can find."
Beale voted at a school in Chicago and Kelly voted early.
Beale touted his record as a job creator for the South Side ward he represents in Chicago's City Council.
That's the reason Juanita Williams, who went to school with Beale, said she voted for him Tuesday, noting that he helped bring a Wal-Mart to the area. The 47-year-old assistant teacher also said Beale has regularly provided school supplies and Christmas gifts to needy students.
Jackson is the third consecutive congressman from the district to leave office under an ethical or legal cloud. He resigned in November after a months-long medical leave for treatment of bipolar disorder and depression.
Voters haven't seen an open primary since 1995, when Jackson first won office.
Turnout at the polls was expected to be low, and candidates and election officials braced for a possible winter storm that could dump up to six inches of snow on the region and complicate Tuesday's logistics. Election officials said they were in communication with streets and sanitation workers about making sure pathways to polls were kept clear.
In Chicago, fewer than 2,800 voters, or roughly 2 percent or registered voters in the district, cast early ballots. In suburban Cook County - the bulk of the district's voting population - it was nearly 2 percent. The last time the Chicago area had a special primary election for Congress was 2009 after Rahm Emanuel left his seat to take a job as White House chief of staff. Roughly 18 percent of registered voters in the district spanning North Side neighborhoods voted. In suburban Cook County, the percentage was far lower.