Black Hawk County

In one of the nation’s whitest states, Waterloo — the biggest city in Black Hawk County — is one of the most diverse communities. And thanks to its sizable African American population, the University of Northern Iowa and a strong organized labor presence, Black Hawk County is reliably Democratic.

In 2016, it was one of just 5 counties in the state to vote for Hillary Clinton over Donald Trump. But Black Hawk County favored Bernie Sanders in the caucuses.

This time around, Amy Klobuchar has been a frequent presence. With his strong support among African Americans, Joe Biden — who visited Saturday — could have a solid showing. This is one place where the constraints imposed on the candidates by the impeachment trial could make a difference: Sanders was forced to cancel a late January rally at UNI due to the Senate’s unforgiving schedule.

Cerro Gordo County

Mason City is one of the must-stops in north Iowa — candidates attended 35 events there in the run-up to the caucuses. And no one spent more time there than Klobuchar, who needs to perform well in the area, just a few miles from her home state, to have any chance of success.

The area is more familiar with her than most since it’s part of the Rochester, Minnesota, media market. On the campaign trail, Klobuchar frequently boasts of her ability to win in rural areas — like the Minnesota counties that border North and South Dakota or Iowa — so those claims will be put to the test here.

But Klobuchar wasn’t the biggest spender in the Rochester media market — that was Andrew Yang, who outpaced everyone with $782,000 in broadcast and cable television buys.

Dubuque County

The city of Dubuque, in northeastern Iowa, is the heart of the state’s Roman Catholic community: It’s home to five nunneries and two Catholic universities, and roughly half the residents are Catholic.

While Sanders’ popularity with organized labor will make him competitive here, this should be Biden Country — he’s a familiar face, visited frequently during the campaign and has played up his Catholic background here. Biden also has the support of popular local Rep. Abby Finkenauer. If Biden’s not winning here, he’s probably having a rough night.

Johnson County

Sanders crushed Clinton in this liberal stronghold in the 2016 caucuses — progressive politics play well in what’s sometimes referred to as the People’s Republic of Johnson County.

Home to the University of Iowa, this should be fertile ground once again for Sanders, who dominates among voters between the ages of 18-49, as well as Elizabeth Warren, who also runs well among younger voters. Both senators made appearances in Iowa City in the final weekend before the caucuses.

Lee County

Iowa has more Obama-Trump counties (31) than any other state, and this is one of them. While there aren’t a lot of delegates at stake in this Mississippi River county in Iowa’s far southeastern corner, it’s a good place to gauge how Pete Buttigieg’s focus on Obama-Trump counties is faring.

Lee is the rare county with not one but two county seats, Fort Madison and Keokuk — and Buttigieg campaigned in both of them.

Linn County

Aside from the Des Moines area, no other place in Iowa received as many candidate visits as Cedar Rapids. Since Sept. 1, each of the four top-tier candidates made at least a half-dozen visits to Linn County and its many blue-collar workers.

The second most populous city in the state after Des Moines, Cedar Rapids went for Barack Obama in the 2008 caucuses and Sanders in 2016. Sanders continues to generate energy here again this year, drawing 3,000 people to a Saturday event. On the same day, Joe Biden had one of his better Iowa crowds of the campaign — but it was only 520 people.

Polk County

This is the biggest prize on caucus night, representing nearly one-fifth of the total state delegates. Home to Des Moines — the biggest city in the state — and key suburbs such as Ankeny, Johnston and Clive, population growth is expected to help drive record turnout here. The Democratic Party already had to move several precinct caucus locations into larger spaces because of potential fire code issues.

The county’s population tends to be wealthier, more diverse and better educated than the rest of the state. In 2016, Clinton beat Sanders here 53 percent to 46 percent. Freshman Rep. Cindy Axne, who represents Polk County, has endorsed Biden, arguing he’s the most likely ticket-topper to help vulnerable Democrats like her get reelected in 2020.

Pottawattamie County

This county is home to Council Bluffs, the second-largest city in western Iowa after Sioux City. It was one of Clinton’s strongest counties in 2008, but Pottawattamie went narrowly for Sanders over her in 2016.

Only one candidate has campaigned here more than Sanders this time around: Klobuchar. The county chair here has endorsed her, and the Minnesota senator’s daughter and husband have tried to keep a steady presence. But Sanders has saturated the Omaha media market that covers the county. And Warren’s foot soldiers have been aggressively organizing at local events and knocking on doors.

Scott County

Home to Bettendorf and Davenport, Iowa’s third-largest city, Scott County was one of Obama’s top counties in the state in 2008. Eight years later, it was one of the rare counties where Sanders and Clinton were nearly tied (with Sanders narrowly topping Clinton, 50.5 percent to 49 percent).

While each of the top four candidates has invested time in this Mississippi River county, both Sanders and Biden see it as a battleground area between their campaigns. But other dynamics could drive local votes: Last year, when the county was among those deluged by ravaging flood waters, Warren was among the first 2020 candidates to visit.

Meanwhile, the biggest spender in the Davenport media market? Billionaire Tom Steyer, who plowed nearly $3.2 million into ads there.

Story County

This college county is anchored by Ames and Iowa State University, which means it’s Sanders Country. He crushed Clinton here in 2016, and his current campaign has swarmed the campus with organizers.

While Story County is not quite as populous as the University of Iowa’s Johnson County, it still gets quite a bit of attention from the candidates. Yang made more visits here than any other candidate, so if he’s not doing well here, he’s probably not making a dent anywhere in the state.

Woodbury County

This was a must stop for every Democratic campaign, since it’s home to Sioux City, the largest city in western Iowa. The area might provide some insight into whether Klobuchar or Buttigieg could out-organize — or at least out-dazzle —Sanders, who beat Clinton here by 7 points in the 2016 caucuses.

Klobuchar has spent lots of time here, tying Sanders for the number of visits to the county. But Buttigieg is close behind them both. Woodbury has a larger Latino population than most of Iowa, making up 17 percent of its residents. And the Sioux City school system is one of the largest employers in the county, making education and union issues particularly important to residents here.