People from Illinois and Chicago are proud of their state and city, but one drawback they can’t shy away from is the unseemly parade of public officials who have gone to prison on corruption charges. And now that Democrats are five weeks away from nominating Barack Obama — a Chicagoan for the past 23 years — some in the party are worried that the aura of corruption could get in his way during the fall presidential campaign.

Republicans have played up links between Obama and Antoin “Tony” Rezko, a Chicago political fundraiser convicted on influence-peddling charges last month and immediately dispatched to federal prison. But Obama and his Chicago supporters say that throughout his public career the senator has been a reformer who stayed outside a political culture that has bred so much corruption.

Some Illinoisans are frank about their state’s image. “We’re a very embarrassed state. It’s sad to say that, because you want to be proud,” said Republican Rep. John Shimkus, who represents the rural, southern end of the state. “The odds are, based on past history, that there’s more signs of problems at senior levels in the executive branch than of success.’’

Shimkus was referring to the fact that of the past nine governors, back to Republican William G. Stratton in the 1950s, four have been indicted and three convicted. One of them, Republican George Ryan, is in federal prison now for racketeering and fraud; the current governor, Democrat Rod R. Blagojevich, is reportedly under investigation in relation to the Rezko case, though Blagojevich denies it.

In heavily Democratic Chicago and surrounding Cook County, the problem has been even more pronounced. In the past three and a half decades — ever since the Justice Department began zeroing in on corruption in the area — scores of aldermen, judges and city employees have been convicted. Democratic Rep. Luis V. Gutierrez, who served on the 50-member City Council before going to Washington in 1993, recalled that at about the time he left, one-third of the council members had been indicted.

This history and Obama’s one-time friendship with Rezko have been a campaign issue. Obama has conceded that he used bad judgment in a 2005 land purchase from Rezko, his friend since the mid-1990s, in a deal that enlarged the yard of the senator’s Hyde Park home. “I consider this a mistake on my part, and I regret it,” Obama told the Chicago Sun-Times in late 2006, but he said he had done nothing wrong.

In May, Obama also warned Republicans that his GOP opponent’s background was fair game. John McCain was one of five senators, known as the “Keating Five,’’ investigated for their links in the 1980s to disgraced savings and loan magnate Charles H. Keating Jr. The Senate Ethics Committee said McCain “exercised poor judgment” but did not term his actions improper.

Charles N. Wheeler III, a longtime journalist who covered Illinois government for decades and now directs the public affairs reporting program at the University of Illinois at Springfield, said that linking Obama with Illinois’ climate would be unfair to the candidate. “For people who don’t understand Chicago and Illinois politics it will matter,” he said. “But people who have a more sophisticated knowledge of Chicago politics will realize that Obama is not a machine hack.”

Obama has always run for office as an outsider who defied the party organization. He won his state Senate seat on the South Side essentially by boxing out the incumbent, Alice Palmer; tried to oust Bobby Rush from Congress in a primary four years later; and then came out of nowhere to win a crowded primary for an open Senate seat in 2004. Instead of coming up through Democratic ward organizations, he was on the University of Chicago Law School faculty and was a community organizer. “Obama isn’t thought of as a rough-and-tumble guy in Chicago,” said another former Chicago alderman, Democratic Rep. Danny K. Davis. “He was a sheltered guy. The guys in the ward organizations call him a babe in the woods.”

And he defended his city: “It’s a different Chicago. A lot of things have changed. There are lots of new people in office who didn’t come up through the traditional route.”

Gutierrez, too, says his hometown is being mischaracterized. “I don’t know that we have that image of ourselves,” he said. “As I travel around, people say, ‘Chicago: such a clean, vibrant growing city.’”