CHICAGO - You need a ticket to attend Barack Obama's outdoor Election Night event in Chicago, but Mayor Richard Daley predicted Tuesday that as many as 1 million people could show up at the lakefront park where the event is being held.

Obama's campaign sent an e-mail Tuesday inviting only supporters from Obama's home state of Illinois. To get tickets, people need to sign up on the Web for a printable ticket that'll be e-mailed before the Nov. 4 event in Grant Park. Only one request per person is allowed to admit the ticket holder and a guest.

It is unclear how many people were invited, but city officials have said the field at the park's south end - the location of the rally - can hold between 60,000 and 70,000 people. Gates open at 8:30 p.m.

Daley told reporters Tuesday he was concerned about the logistics and expected as many as 1 million people.

"It's going to be surprising, there are going to be a lot of people who want to come down to celebrate, yes there will be (a million) we hope its a million or more, that's realistic." Daley said. "It's going to be wonderful."

Chicago officials have said the event could cost $2 million, if not more, but the Obama campaign has assured them they will pay.

Also Tuesday, city officials announced that Neil Sullivan, who helped coordinate security at the 2005 World Series in Chicago, will also take a security role at the Obama rally.

Sullivan was hired on a 90-day temporary contract in September to help with security for the White Sox and Cubs playoff runs, said Office of Emergency Management and Communication spokeswoman Jennifer Martinez.

When both teams fell in the first round of the playoffs, officials decided to use Sullivan for election night logistics, Martinez said.

The Chicago Police Department has also canceled days off for all its officers on Election Day, spokeswoman Monique Bond said.