601 Union St, Seattle, WA 98101

Office · Seattle · Seattle-Bellevue metro, WA

One of 1,701 reachable office buildings in Seattle. Larger than 100% of office buildings in Seattle (median 8,568 SF), derived from assessor records.

Usable building area
1,141,886 SF, King County Assessor
County gross area
1,607,844 SF, King County Assessor
Excluded area
465,958 SF outside primary usable area
Lot size
89,950 SF, King County Assessor
Year built
1989, King County Assessor
Stories
56, King County Assessor
Predominant use
Office Building, King County Assessor
Assessed value
$365,997,600, per the King County Assessor (not a market appraisal)
Assessed value per usable SF
$320.52/SF, derived from assessor records
Usable area / lot
12.69, derived from assessor records
Vintage
1980s vintage
Zoning
DOC1 U/450/U, King County
County use code
Office Building

Nearby comparable buildings

Same building type, by distance. Assessor facts only; not an opinion of value.

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Sale history and market context

MakeMe Estimate: $316M (estimated market value), with a likely range of $270M to $369M (half of recent verified sales in this segment landed inside that range). Based on 1 verified arm's-length comparable sales (through 2026-06-01). Not an appraisal. How this estimate works.

lower confidence: 1 comparable sale within 3 miles; nearest 0.5 mi. This property type carries wider measured error; treat the estimate as a starting point.

Comparable sales used as evidence

Recorded arm's-length sales of similar buildings nearby; nearer and more recent sales rank first. Buyer and seller names are withheld. Get this data via API.

Market context: Office in Seattle

median verified sale $364.58/SF over the trailing 24 months; 28 sales in the last 12 months and 52 in 24 (newest verified sale 2026-05); the middle 80% of recent sales traded at 0.63x to 1.44x their county assessed value, median 1.00x (52 sales with usable county values).

  • 2022: $472.22/SF median (35 sales)
  • 2023: $415.77/SF median (20 sales)
  • 2024: $326.92/SF median (24 sales)
  • 2025: $371.06/SF median (27 sales)
  • 2026 YTD: $390.03/SF median (11 sales)

This estimate sits at 0.86x county assessed value, the 27th percentile of those recent sale premiums.

Computed from 1,574 verified arm's-length sales in King County public records (52 in the trailing 24 months). Free public records. Not an appraisal.

Source: King County recorded sales extract; buyer and seller shown only when a company or organization. Individual names are withheld.

Value over time

$0$500M$1B$1.5B201120142017202020232026$316M$366MCounty assessed valueMakeMe Estimate range

Dark line: county assessed value per King County tax rolls. Blue line: our estimate; dashed years are a modeled backcast built from recorded arm's-length sales in the building's segment, not estimates published at the time, and years without enough sales stay unmodeled. The shaded range is the model's measured error band; about half of verified sales in the segment land inside it. Not an appraisal. How this estimate works.

Land, site, and value history

Assessed value moved from $303,010,000 (2011) to $365,997,600 (2026), up 21% over 15 years, per county tax rolls. The 2026 roll splits $365,997,600 into $143,416,300 land and $222,581,300 improvements.

Taxes

Permit history

Source: King County permit records (newest first).