City · Washington
Black Diamond, Washington
Black Diamond, city, in King County, Washington. Black Diamond had 6,978 residents on July 1, 2025 by the Census Bureau's estimate, up 48.6% since 2020; the 2020 Census counted 4,697 and the ACS 2020-2024 5-year estimates put it at 5,961 (±26). GEOID 5306330.
Residents, July 2025 estimate
6,978
Census Bureau estimate (no margin published)
2020 Census count: 4,697 · ACS 2020-2024: 5,961 ±26
Median household income
$141,383
±$13,982 (90% margin)
Washington: $98,141
Median home value
$779,100
±$58,019 (90% margin)
Washington: $564,600
Median gross rent
$1,453
±$1,098 (90% margin)
Washington: $1,760
Where is Black Diamond and what county is it in?
Black Diamond is a city in King County, Washington. It covers 6.6 square miles of land, 712 residents per square mile in 2020.
Black Diamond is in the Seattle-Tacoma-Bellevue, WA metropolitan statistical area, which takes in 3 counties (Census Bureau delineation, July 2023).
Source: 2024 Gazetteer and 2020 place-by-county files, U.S. Census Bureau · Census reference files
How many people live in Black Diamond, and is it growing?
The Census Bureau estimates that 6,978 people lived in Black Diamond on July 1, 2025, up 48.6% since 2020, faster than Washington (+3.8%). The 2020 Census counted 4,697 residents. The 2020-2024 American Community Survey, a five-year sample, puts the population at 5,961 (±26).
The yearly series starts from the Census Bureau's July 2020 estimate, 4,846, which differs from its April 2020 base of 4,695 (in 2020 the estimates dipped in many college and military towns), so the first step is large; the change since 2020 above is measured from the April base.
| Measure | Black Diamond | King County | Change since 2015-2019 |
|---|---|---|---|
| Total population | 5,961 ±26 | 2,287,171 | +1,485 |
| Households | 2,316 ±153 | 941,054 | +557 |
| Average household size | 2.57 ±0.17 | 2.39 | no clear change |
| Housing units | 2,442 ±157 | 1,003,284 | +620 |
Black Diamond's population since 2000
From 3,970 in 2000 to 6,978 in 2025: up 75.8%. The 2000, 2010 and 2020 figures are census counts, each for Black Diamond as it was drawn that year: a place that annexed land, or a community that has since incorporated, covered a different area then. The 2005 figure is the Census Bureau's intercensal estimate, revised to fit the 2000 and 2010 counts and drawn on 2010 boundaries; 2015 and 2025 are July 1 estimates made from the census before them.
Source: The 2000, 2010 and 2020 Census counts and the Census Bureau's population estimates (intercensal 2000-2010, Vintage 2020, Vintage 2025) · Census population estimates
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026); Census PEP Vintage 2025 (SUB-EST2025, CO-EST2025); 2020 Census P.L. 94-171 · Check it at data.census.gov
Who lives in Black Diamond?
The median resident of Black Diamond is 38.1 years old; 24.9% are under 18 and 10.2% are 65 or older. The largest group is non-Hispanic white residents at 67.0%, then non-Hispanic Asian residents at 17.6%. 19.0% of residents were born outside the United States.
| Measure | Black Diamond | King County | Change since 2015-2019 |
|---|---|---|---|
| Median age | 38.1 ±3.9 | 37.4 | no clear change |
| Under 18 years | 24.9% ±3.8 pts | 19.5% | – |
| 65 years and over | 10.2% ±3.9 pts | 14.0% | – |
| Male | 52.2% ±3.5 pts | 50.7% | – |
| Hispanic or Latino (any race) | 7.9% ±4.7 pts | 11.0% | no clear change |
| White alone, not Hispanic | 67.0% ±7.1 pts | 52.9% | −19.8 pts |
| Black or African American alone, not Hispanic | 0.4% ±0.6 pts | 6.4% | – |
| Asian alone, not Hispanic | 17.6% ±6.7 pts | 20.5% | +14.2 pts |
| American Indian and Alaska Native alone, not Hispanic | 0.0% ±0.7 pts | 0.4% | – |
| Native Hawaiian and Other Pacific Islander alone, not Hispanic | 0.0% ±0.7 pts | 0.7% | – |
| Two or more races, not Hispanic | 6.4% ±3.6 pts | 7.3% | – |
| Some other race alone, not Hispanic | 0.6% ±0.9 pts | 0.6% | – |
| Born outside the United States | 19.0% ±5.9 pts | 25.8% | +9.5 pts |
| Speak a language other than English at home (age 5+) | 18.0% ±6.0 pts | 31.1% | – |
| Civilian veterans (age 18+) | 5.9% ±2.6 pts | 4.5% | – |
| With a disability | 8.2% ±2.9 pts | 10.3% | – |
| No health insurance coverage | 2.5% ±2.8 pts | 5.2% | – |
| High school graduate or higher (age 25+) | 97.7% ±1.5 pts | 93.8% | – |
| Bachelor's degree or higher (age 25+) | 54.7% ±6.7 pts | 56.7% | +13.0 pts |
| Graduate or professional degree (age 25+) | 17.9% ±5.0 pts | 24.2% | – |
| Lived in the same house a year earlier | 86.6% ±5.3 pts | 83.3% | – |
| Moved from another state in the past year | 4.4% ±2.8 pts | 3.5% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profiles DP02, DP05) · Check it at data.census.gov
What do households in Black Diamond earn?
Half of Black Diamond's 2,316 households earn less than $141,383 a year (±$13,982), against $124,746 in King County and $98,141 in Washington. In 2015-2019 it was $133,518 in 2024 dollars; the margins of error cannot tell the two periods apart.
| Measure | Black Diamond | King County | Change since 2015-2019 |
|---|---|---|---|
| Median household income | $141,383 ±$13,982 | $124,746 | no clear change |
| Mean household income | $166,104 ±$16,078 | $176,799 | – |
| Per capita income | $65,562 ±$6,944 | $74,100 | no clear change |
| People below the poverty line | 2.1% ±2.1 pts | 8.6% | – |
| Children under 18 below the poverty line | 2.5% ±4.2 pts | 9.7% | – |
| Households receiving SNAP | 2.1% ±2.4 pts | 8.2% | – |
| Households with a computer | 100.0% ±1.7 pts | 98.1% | – |
| Households with a broadband subscription | 95.9% ±3.5 pts | 95.1% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP03) · Check it at data.census.gov
What does housing cost in Black Diamond?
Owners occupy 86.0% of Black Diamond's occupied homes and renters 14.0%. The median owner-occupied home is valued at $779,100 by its owner (±$58,019).
| Measure | Black Diamond | King County | Change since 2015-2019 |
|---|---|---|---|
| Median home value (owner-occupied) | $779,100 ±$58,019 | $859,900 | +$270,700 |
| Median gross rent | $1,453 ±$1,098 | $2,092 | – |
| Renters paying 35% or more of income on rent | 22.4% ±19.1 pts | 37.5% | – |
| Median monthly owner costs, with a mortgage | $3,068 ±$233 | $3,273 | – |
| Owner-occupied homes | 86.0% ±5.4 pts | 55.4% | no clear change |
| Renter-occupied homes | 14.0% ±5.4 pts | 44.6% | – |
| Housing units | 2,442 ±157 | 1,003,284 | +620 |
| Homeowner vacancy rate | 0.0% ±2.0 pts | 0.7% | – |
| Rental vacancy rate | 0.0% ±11.6 pts | 5.3% | – |
| Single-family detached homes | 84.9% ±6.4 pts | 50.0% | – |
| Mobile homes | 2.6% ±2.7 pts | 1.4% | – |
| Built 2020 or later | 23.2% ±6.5 pts | 2.1% | – |
| Built 2010 to 2019 | 17.7% ±5.2 pts | 14.2% | – |
| Built 1939 or earlier | 5.8% ±3.1 pts | 10.9% | – |
| Households with no vehicle | 3.5% ±3.5 pts | 11.2% | – |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP04) · Check it at data.census.gov
How many new homes is Black Diamond building?
Builders took permits for 205 new housing units in Black Diamond in 2025 (205 in single-family houses), 29.4 per 1,000 residents against 4.4 across Washington.
Counts of units in permits a local office issued; not every permitted unit is built. A year marked with months was reported for part of the year.
Source: Building Permits Survey, annual place files 2019-2025, U.S. Census Bureau · Census Building Permits Survey
How do people in Black Diamond work and get to work?
63.9% of Black Diamond's workers drive alone and 24.9% work from home. The average trip to work takes 37.5 minutes.
| Measure | Black Diamond | King County | Change since 2015-2019 |
|---|---|---|---|
| In the labor force (age 16+) | 74.1% ±4.6 pts | 69.9% | – |
| Unemployment rate | 1.3% ±1.2 pts | 4.8% | – |
| Drove alone to work | 63.9% ±7.9 pts | 50.4% | – |
| Carpooled | 8.9% ±6.7 pts | 7.0% | – |
| Public transportation | 0.2% ±0.5 pts | 6.8% | – |
| Walked | 0.8% ±0.9 pts | 4.3% | – |
| Worked from home | 24.9% ±7.4 pts | 29.2% | +16.8 pts |
| Mean travel time to work | 37.5 min ±4.4 | 27.6 min | no clear change |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) (Data Profile DP03) · Check it at data.census.gov
What census tracts are in Black Diamond?
1 census tract lies mostly in Black Diamond, and 2 more reach into it (2020 census blocks).
| Tract | Residents, 2020-2024 | Median household income |
|---|---|---|
| Tract 316.03King County | 7,941 | $144,573 |
| Tract 316.05King County | 3,973 | $146,750 |
| Tract 315.01King County | 4,066 | $144,773 |
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026); 2020 block assignment files (tract share = share of the tract's census blocks in Black Diamond) · Census block assignment files
How does Black Diamond compare with other places in Washington?
By the Census Bureau's July 2025 estimates, Black Diamond is the 4,076th-most populous of the 19,476 U.S. incorporated places that have one and the 111th-most populous of 281 in Washington.
Black Diamond ranks 61st of 387 places in Washington with 1,000 or more residents and a reliable estimate, by median household income.
| Measure | Rank | Of |
|---|---|---|
| Population, July 2025 estimate | 111th | 281 |
| Growth 2020-2025 (PEP) | 3rd | 203 |
| Residents per square mile | 303rd | 394 |
| Median household income | 61st | 387 |
| Per capita income | 62nd | 393 |
| Median home value | 67th | 384 |
| Bachelor's degree or higher | 41st | 382 |
| Median age | 228th | 394 |
| Owner-occupied share | 88th | 388 |
| Work from home | 76th | 307 |
| Travel time to work | 34th | 394 |
Black Diamond's figures with every place in Washington (CSV)
Every place in Washington, sortable · Compare Black Diamond with other places
Source: PlainCities ranks computed from the American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026) and PEP Vintage 2025 · How ranks are computed
How reliable are the figures for Black Diamond?
18 of the 57 figures for Black Diamond on this page carry a coefficient of variation over 40% and are marked with a ring: they come from a small sample, so read them as rough.
The American Community Survey samples about one household in eight over five years, so every figure is an estimate with a 90% margin of error (shown under each value). A ring marks an estimate whose coefficient of variation is over 40%. A change is called only when the gap between the two periods is larger than their combined 90% margin (the square root of the sum of the two squared margins), the Census Bureau's test. How to read a margin of error.
Source: American Community Survey 2020-2024 5-year estimates, U.S. Census Bureau (released January 2026): margins of error as published · ACS technical documentation
How these figures are made: methodology and release checks · reading a margin of error · every state · corrections
Not on this page: crime, weather and schools for Black Diamond are other agencies' records. Crime: the FBI's Crime Data Explorer · climate: NOAA's U.S. Climate Normals · schools: the National Center for Education Statistics' public schools in Black Diamond.