Research
ZIP Code Research
Each analysis is computed from the PlainZIP database (Census, FHFA and IRS files), states its method and its limits, and leads with what it found.
Analyses
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PlainZIP analysis
Where Household Incomes Rose, ZIP by ZIP
Of the 18,536 residential ZIP codes whose boundary held and whose incomes can be compared, 2,643 (14.3%) saw median household income rise from 2015-2019 to 2020-2024 by more than the surveys' margins of error, in 2024 dollars; 892 (4.8%) saw it fall, and the rest cannot be told apart from no change. Chance alone would put about 927 ZIP codes on each side at this confidence even if nothing had changed: the rises are about 1,716 more than chance, the falls are within it.
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PlainZIP analysis
ZIP Codes That Cross County Lines
9,447 of the 33,774 residential ZIP codes of the 50 states, D.C. and Puerto Rico (28.0%) have at least 1% of their land in a second county (Census 2020 ZCTA-county relationship file). A ZIP code follows postal delivery routes, not county borders.
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PlainZIP analysis
Home Prices by ZIP Code, 2015 to 2025
In the 15,625 ZIP codes where FHFA reports a house price index for both 2015 and 2025, the median ZIP saw prices rise 92% over the ten years.
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PlainZIP analysis
Income Gaps Between the ZIP Codes of the Big Postal Cities
Among the 50 postal city names with the most residential ZIP codes, the ZIP codes named Cincinnati, OH are furthest apart: median household income in 45243 is 8.4 times that in 45225. A postal name reaches past the city's legal limits, so these are gaps between the ZIP codes that use the name, suburbs included, not inside the city itself.
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PlainZIP analysis
The Richest ZIP Code in Every State
By IRS adjusted gross income per tax return the richest residential ZIP code in the U.S. is 33109 in Fisher Island (Miami Beach), FL, at $4,403,678 (2022); by income per person it is 10007 in New York, NY, at $212,686; by median household income 69 ZIP codes tie at the Census cap of $250,000 or more (ACS 2020-2024). This study gives every state's leader by each measure; in 15 states the median leader sits at the cap, and in 18 states the per-person and median measures name the same ZIP code.
Source: PlainZIP analyses of U.S. Census Bureau, FHFA and IRS data; methods on each page and on the methodology page.