Four years ago, Obama made his announcement in Springfield. On Monday, he announced his intentions to run through a video on his website with his new campaign slogan, "it begins with us."
The official start of President Obama's second White House bid comes 20 months before the November 2012 election.
BarackObama.com launched the video before dawn on the fourth day of the fourth month to symbolize the 44th president's re-election effort.
The president is getting a head start on the Republicans who so far are without a clear frontrunner for their 2012 nomination.
The Obama campaign will be headquartered in the historic Prudential building near Chicago's lakefront and will include several faces familiar from the president's successful 2008 run:
Bonus help is available from former Obama chief of staff, mayor-elect Rahm Emanuel, who will be working a few blocks away at City Hall.
"I will help the president. I'm pleased that Chicago will be the headquarters. But my first and primary goal will be what the voters asked me to do which is to solve the problems facing them here, immediately at home," Emanuel told ABC7.
"Not just the president, people from the Democratic National Committee, all the key decision makers from the party and a lot of major fundraisers. That's going to mean major clout and power is going to be right here in Chicago," said Laura Washington, ABC7 political analyst.
In the race to 2012, the GOP will play up an unemployment rate near 9 percent, the controversial health care law and the fact the U.S. is now involved in three wars, including Libya.
Illinois Republicans will try to bring their party's presidential candidates to town by holding a statewide primary poll on November 5.
"Support for the president has been falling, that's pretty good grounds for a Republican challenger," said Sen. Mark Kirk, (R) Illinois.