It’s been nearly 30 years since Washington sent a Republican to the U.S. Senate, and that pattern doesn’t look like it’s changing anytime soon.

As my colleague Danny Westneat pointed out in a recent column, King County, overwhelmingly Democratic and home to nearly 30% of Washington’s population, is the Republican’s stumbling block in statewide elections.

And that made me wonder: Just how “blue” is King County compared with other U.S. counties?

Answering that question is a little tricky. Washington is among 19 states where voters register without reference to party, so there’s no official count of Democrats, Republicans and Independents here.

You can look at election results, of course. In 2020, President Joe Biden won around 75% of the vote in King County. And in Tuesday’s U.S. Senate race, Democrat Patty Murray cruised to another term with a similar margin of victory in King County against Republican challenger Tiffany Smiley.

While that’s certainly an indication that this is a very blue place, it doesn’t truly tell us about political identity. Many people who cast their vote for Biden or Murray might not consider themselves Democrats.

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I turned to data from market research firm Nielsen, which conducts nationwide surveys on political party affiliation. I compared the 100 largest U.S. counties (ranked by the number of registered voters) based on the percentage of voters who identify as Democrats, or as Independents who feel closer to Democrats.

Nielsen surveyed more than 170,000 adults from December 2020 to April 2022, including nearly 2,900 in King, Snohomish and Pierce counties.

The data shows in King County, Democrats outnumber Republicans by more than 4 to 1.

Nearly 1.1 million voters said they were Democrats or Democratic-leaning Independents — around 68% of the county’s 1.6 million registered voters. Only around 250,000, or 15%, identified as Republicans or leaned Republican. Independents who do not lean to the left or the right total about 160,000, or 10%. And another 110,000 registered voters, or 7%, identified with some other political party affiliation, such as Libertarian, Green Party, etc.

King is overwhelmingly blue, but there are some big counties that are even bluer. Among the 100 counties, King ranked 9th.

In Prince George’s County, Maryland, which is outside of Washington, D.C., 77% of registered voters were Democrats or leaned Democratic, making it the bluest of the large counties. San Francisco is both a city and county, and as a county, it ranked second behind Prince George’s. And in third, fourth and fifth place were three of New York City’s boroughs which are also counties: Bronx, Kings (Brooklyn), and New York (Manhattan), in that order.



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Snohomish and Pierce were also among the 100 counties with the most registered voters, and Snohomish is by far the bluer of the two. Of the county’s 582,000 voters, 346,000 (or 55.5%) said they’re Democrats or they lean Democratic — that ranked Snohomish as the 21st-bluest large county. Pierce ranked 71st. Of its 601,000 voters, only 267,000 (or 44.5%) were Democrats or leaned Democratic.

The reddest big county was Brevard in Florida, located just east of Orlando, where 51% of registered voters are Republicans or Independents who feel closer to Republicans. Salt Lake County in Utah ranked second, and Florida’s Lee County, located on the Gulf Coast, was third.

There were more than 92 million registered voters in the 100 largest counties, and overall, they were a lot more blue than red. This isn’t surprising, as a lot of these counties are located in major urban areas that tend to be more Democratic. For example, Los Angeles, by far the most-populous U.S. county, is home to 6.6 million registered voters. Around 64% were Democrats or leaned Democratic.

In total, about 53% of voters in the 100 big counties were Democrats or leaned Democratic, compared with just 28% who were Republican or leaned Republican. Ten percent were Independents who leaned neither left nor right, and 9% identified with some other political affiliation.