President Barack Obama carried the county in 2008, the first Democratic presidential candidate to do so since 1964. Mitt Romney's campaign is determined to win it back.
"One of the ways you swing a county like Hamilton County back is a lot of shoe leather," said Scott Jennings, Ohio campaign director for the Republican presidential candidate. "We're spending a lot of time there."
The stakes are high. It's the biggest battleground county in Ohio, the closely contested swing state considered likely to be crucial to winning the White House next Tuesday.
"Hamilton County is one of the most important places in America," Jennings said.
On that point, both sides agree.
"Traditionally, Hamilton County has been a firewall for the GOP in Ohio, and when they lost here in 2008, it made a huge difference," said Caleb Faux, executive director for the county Democratic Party. "If they lose it this year, their chances of carrying Ohio become very slim, and if they don't carry Ohio, their chances of winning nationally are very slim."
Both sides are focusing major get-out-the-vote efforts in Cincinnati and its suburbs, and the candidates, their running mates and surrogates have campaigned here frequently. There also has been heavy national news media presence.
Obama will lead a major rally this Sunday at the University of Cincinnati basketball team's arena. Romney and running mate Paul Ryan head a rally laden with GOP officeholders, past officials and star athletes Friday evening in West Chester, just over the county's northern border and in the Cincinnati television market.
Obama got 225,213 votes in the county in 2008, nearly 30,000 more than John McCain. George W. Bush had 222,616 in 2004, nearly 23,000 more than John Kerry. Both carried Ohio.
Local Republicans say they have lost thousands of voters in the past couple decades who have moved to suburbs in the neighboring counties of Butler, Clermont and Warren, fortifying a Republican stronghold.
Cincinnati has a second-term Democratic mayor, Mark Mallory, who's a strong Obama supporter. This is also the home turf of Romney's Ohio chairman, U.S. Sen. Rob Portman, who can call on a network of supporters built up since he first ran for Congress in 1993.
The Romney campaign sees a boost in the lack of competitive congressional races locally. Democrats poured national resources into the area in 2008 to help state legislator Steve Driehaus unseat seven-term Republican Rep. Steve Chabot. Chabot won the seat back in a 2010 Republican-dominated election, and redistricting after the 2010 census has made the seat look secure for the GOP.
Democrats think there is still fallout among the public union workers over the Republican-led effort in 2011 to restrict their collective bargaining. A Cincinnati firefighter, Doug Stern, who said he was a former longtime Republican spoke for Obama at the Democratic National Convention.
"It's still lingering under the radar," Faux said of the resentment for the move against public employees. "I think there a lot of people who haven't forgotten."
In the waning days of the campaign, pro-Romney radio ads in the Cincinnati area have courted swing voters by emphasizing Romney's record as Massachusetts governor in working with legislative Democrats. In one, veteran Hamilton County Prosecutor Joe Deters says he believes Romney will work with both Democrats and Republican to get things done to help Cincinnati.
Both sides have been out knocking on doors or making phone calls. The Obama campaign has eight field offices in the county, up from three in 2008. The Romney campaign says it's running well ahead of 2008 voter contacts for McCain in the country, knocking on 136,000 doors in the past four weeks. .
On a recent evening, staffers and volunteers canvassed blue-collar neighborhoods that were split almost evenly between Obama and McCain in 2008 in working-class Norwood. There were more Halloween decorations than political yard signs, but they found a few supporters.
"Defense is first, then the economy," said Dan Biron, 58, a retired Army major who said he has voted mostly Republican and couldn't vote for Obama.
"I want to have everything on top of the table," he said. "I want to have leadership I can trust."