Clooney and Zellweger entertained a crowd of maybe 100 Minnesota media people, and dozens of other city residents who apparently knew what strings to pull to get inside the Duluth Depot.
The movie was shot a year ago in North and South Carolina, where producers took advantage of some financial incentives.
Clooney said the Carolinas had communities with the 1920s look they needed. And he said the Southern states also provided somewhat more agreeable weather.
"We actually came to Duluth. We thought about shooting here, but it was in February. And, apparently here, from what I understand, it's cold in February," said Clooney.
"Leatherheads" is a romantic comedy based around a fictional Duluth NFL football team, the Bulldogs.
Actor George Clooney directed, and plays the part of Dodge Connolly, an aging playboy of a football player with the Duluth franchise.
Actor John Krasinski, from the TV show "The Office," plays a hotshot football star and war hero recruited to save the ailing Duluth franchise.
Renee Zellweger plays Lexie Littleton, a big city reporter who's bent on exposing the war hero as a fake.
The city of Duluth isn't depicted much beyond a football field and an ornate hotel, but the name is dropped liberally through the film.
Some have wondered why the movie football team is named the Bulldogs. Duluth's 1926 NFL franchise was actually called the Eskimos -- a team that eventually became today's Washington Redskins.
"We wanted to call them the Eskimos, but because we were drinking in the movie, the NFL said we couldn't use the actual names," said Clooney. "You know, they don't drink in the NFL. I was shocked to hear. I couldn't believe it. I was watching a 'Bud' commercial, I think, at the time."
Clooney took most of the press conference questions, and delivered most of the punch lines. Renee Zellweger was asked her impressions of Duluth, a city she'd never visited before.
"Such a rich history here. It was kind of interesting to learn a little bit about it. But that's only been in the 12 hours that we've been here," Zellweger said. "I plan to take a walk before we get on a plane out of here, and just have a little look at the harbor, because it's kind of pretty."
"She's not taking a walk. We're not going to let her," Clooney joked.
But the two did walk out front of the Depot to Duluth's Michigan Street, where a few hundred people were waiting. Some of them were out there at the crack of dawn, saving a spot.
Nicki Patnaude of Duluth spent her lunch hour waiting on a plaza that overlooks the crowd on Michigan Street.
"This is so cool. I've never seen anything like this in Duluth, so I'm really excited," said Patenaude, "To just know that George Clooney and Renee are in our town, and here to promote a movie that's based about something in our town."
The early fans had the right idea. It was well publicized that Clooney and Zellweger would meet fans at 1 p.m. But they were out front 45 minutes before that, and on their way out of town by 12:30.
The movie "Leatherheads" opens in theaters nationwide April 4.