There is speculation Obama will use that event to introduce his running mate in the race for president.
Senator Obama himself reportedly came up with this idea, and the city of Springfield was called only Monday about it. Officials there quickly OKed the plan, and since then, a mad scramble has been underway.
On Tuesday afternoon, the cobblestones that separate the old state capitol and the historic buildings that include Abraham Lincoln's law office were power washed. There will be intense work over the next three days.
"We have a lot of work. It's way worth it for the senator to come back to town. It's nice and we'll work hard together and get all the work done," said Darrell Jackson, Springfield city worker.
"Obama got his start here with politics and came here to announce his candidacy and now he's coming back here, that's great. He's got a lot of supporters here," said Garrett Moffett, Springfield tour guide.
Obama went to Springfield in January of 2007 to announce his candidacy for president. By all accounts, back then, he was the longest of long shots. Despite single-digit temperatures in the area that day, the man drew a crowd estimated to be anywhere from 14,000 to 17,000 people. This August weekend, the mayor of Springfield said he expects an even larger turnout.
"We don't know what to expect on Saturday. Our count was somewhere between
14,000 and 17,000 on that cold day, one of the coldest days in the history of the city of Springfield, and we still had 14,000 to 17,000 people here. So we would certainly expect a lot more than that," said Mayor Tim Davlin, Springfield.
It's unknown if Obama would already have announced the name of his vice presidential nominee by Saturday, but it will be the veep candidate's first joint appearance.
Those believed to be on his short list also were keeping mum. Kansas Gov. Kathleen Sebelius, rumored as a possible choice, professed no inside knowledge of when word would come.
Obama addressed the Veterans of Foreign Wars in Orlando, Fla., Tuesday morning and didn't reveal his choice. He praised Sen. Joseph Biden of Delaware, the Senate Foreign Relations Committee chairman thought to be among the contenders, for proposing an additional $1 billion of reconstruction projects in the Republic of Georgia after the Russian invasion.
Then Obama headed off for a bus tour of North Carolina and Virginia to discuss economic issues through Wednesday, leaving his schedule open at the end of the week for an announcement. The Democratic National Convention is set to begin next Monday.
The list of potential running mates is widely believed to be down to four names: Sebelius, Biden, Virginia Gov. Tim Kaine and Indiana Sen. Evan Bayh. Obama's major rival for the nomination, Sen. Hillary Rodham Clinton of New York, was seen by some Democrats as a longshot pick.
In Warren, Mich., on Tuesday, Sebelius wouldn't say if she expects to be chosen and said she doesn't know the timetable for naming Obama's choice. "I think a week from tomorrow we will all know," she said.
Sebelius spoke to The Associated Press by telephone before telling a town hall meeting at Macomb Community College that "Barack Obama has been a very strong champion of equal pay for equal work." She accused his Republican rival, Sen. John McCain, of frequently opposing "the opportunity for pay equity bills to move through Congress."
Only Obama, his wife, Michelle, a handful of his most senior advisers and his two-member search committee know for certain who has been vetted and discussed. Staffers were already in place to aid Obama's pick, including more than a dozen seasoned operatives who have set up shop in a section of the campaign's Chicago headquarters.
Campaign manager David Plouffe has said that Obama supporters would receive first word of Obama's decision through a mass text message, but otherwise the team has revealed little about what to expect. Historically, presidential tickets then tour battleground states to maximize media exposure, and Obama is expected to do the same.
A similar decision looms for McCain. In hopes of grabbing the post-convention spotlight from Obama, McCain is considering naming his running mate in the few days between when the time Democrats leave Denver and when the Republicans begin their nominating convention in St. Paul, Minn.
McCain's top contenders are said to include Minnesota Gov. Tim Pawlenty and former Massachusetts Gov. Mitt Romney. Less traditional choices include former Pennsylvania Gov. Tom Ridge, an abortion-rights supporter, and Connecticut Sen. Joe Lieberman, the Democratic vice presidential pick in 2000 who now is an independent.
Lieberman has been traveling with McCain on his campaign plane recently.
Pawlenty was gearing up for a weekend campaign swing in Ohio and Pennsylvania on behalf of McCain and said he might travel to Denver next week as a McCain surrogate during the Democratic National Convention.
The Associated Press contributed to this report.