Over the past decade, King County — like the United States as a whole — has become a more racially diverse place.

But diversity across a large geographic area like King County doesn’t necessarily mean there’s a lot of diversity at the neighborhood level. And indeed, there is a wide range in the degree of racial diversity from neighborhood to neighborhood.

For this column, I used a tool called the diversity index. It measures how likely it is that two people who live in the same area, chosen at random, would be of a different race. I calculated a diversity-index score for each of King County’s nearly 400 census tracts, using newly released data on race and ethnicity from the U.S. Census Bureau.

The higher the diversity-index score, the more diverse the neighborhood. A low score means most residents are of the same race.

If there were a neighborhood where 100% of the residents had the same racial background, it would score a zero on the diversity index. We don’t have any place like that in King County, but we come pretty close: The southern half of Vashon Island scored an 8.5. About 96% of residents are white here.

Another interesting fact about this area: It’s one of the oldest census tracts in the county, with more than half the population over age 50. That’s not too surprising, since a much higher percentage of the county’s older residents are white when compared with younger generations, who are more racially diverse (particularly those under 25).

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In case you’re wondering, the northern half of Vashon Island is only slightly more diverse than the southern half. Other areas with the lowest diversity are in the less densely populated eastern parts of the county (Hobart, Duvall, Skykomish), which are also mostly white.

Within Seattle city limits, the lowest level of diversity is a tie between wealthy Madison Park/Broadmoor and West Seattle’s Fauntleroy/Gatewood area. In both, 89% of residents are white.

So where is the greatest level of diversity in King County?

Primarily in the areas south of Seattle. The census tract that had the highest diversity-index score (79) is in the northern end of Federal Way. In this neighborhood, no single racial group makes up more than 28% of the population.

This is also one of the youngest census tracts in the county. The median age here is 30, more than 20 years younger than that part of Vashon Island with the lowest diversity. It is also a far less affluent place, and more than 70% of households here are renters.

Other highly diverse areas are located in White Center, SeaTac and other South County cities that, it should be noted, also tend to have lower median incomes.

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Within Seattle city limits, the most diverse place is Rainier Beach/Dunlap in south Seattle.

These neighborhoods score very high on the diversity index because no one racial group makes up the majority of the population. Only about 30% of King County’s census tracts are like this.

In the other 70% of census tracts, there is a a single majority group. In nearly all of these tracts, white people are the majority. But there are nine tracts that are majority Asian. (There is also one census tract in south Auburn where people of Hispanic ethnicity are close to making up the majority, at 47%).

The diversity-index calculation is based on census racial and ethnic data for eight categories: Black, white, Asian, Pacific Islander/Native Hawaiian, Native American/Alaska Native, Hispanic, multiracial and people who identify as some other race.

Overall, the city of Seattle is less racially diverse than the surrounding King County. Additionally, since 2010, the suburbs have diversified at a significantly faster pace than the city.

For 2018, Seattle’s diversity-index score is 56.5, up more than three points from 2010. But for surrounding King County, the 2018 index score of 62.6 represents an increase of more than seven points.

One major difference between the city and the suburbs is the trend in the white population. In Seattle, the number of white people grew by about 66,000 since the start of the decade, a 16% increase. But in surrounding King County, the white population actually declined by close to 12,000, down more than 1%.

The decline is likely related in part to the fact, alluded to earlier, that white people are an older population than all other racial/ethnic groups. (This is particularly true in King County outside of Seattle — within the city, the white population has a lower median age). An older population has a higher mortality rate, of course. Another factor is that older people often move away from the area after they retire.

In both Seattle and King County, the Asian population has had the biggest increase since 2010. Hispanic and multiracial populations also increased at a faster rate than the white population in both the city and the suburbs.

While Seattle did diversify in the past decade, it remains less racially diverse than most major U.S. cities. Our diversity-index score for 2018 is the 13th lowest among the 50 most-populous U.S. cities. Portland, where 70% of residents are white, is significantly less diverse, with the fourth lowest score.

The least-diverse major city is El Paso, Texas, where 82% of the population is Hispanic. Oakland, California ranks as the most diverse — no single racial/ethnic group makes up more than 29% of the city’s population.


Correction: An earlier version of this column misstated that the Black population grew faster than the white population in both the city of Seattle and in King County outside of Seattle. The Black population only grew faster in the county.