Idaho's households saw the largest income gains over the last decade — and the lead survives a cost-of-living adjustment, though it's a close race with a handful of other Sun Belt/Mountain West states

Summary

Over the last ten years for which full data exists (2014-2024), Idaho households saw the largest increase in median household income of any state: nominal median household income rose from $47,861 to $81,166, a 69.6% increase — well above the roughly 32.5% cumulative rise in the national all-items Consumer Price Index (CPI-U) over the same span. Idaho keeps its #1 rank after accounting for the cost of living: dividing income by each state's own BEA Regional Price Parity (RPP), Idaho's cost-of-living-adjusted growth is +66.4%, still the highest in the country — and its lead over several close nominal competitors (Oregon, Florida, Arizona) actually widens under this adjustment, because those states' own cost of living rose faster than Idaho's did.

One important caveat: Idaho's lead is a point-estimate lead, not a statistically bulletproof one. Because ACS estimates carry sampling error, Idaho's growth rate is not statistically distinguishable from Oregon's (66.9%, p=0.47), Florida's (63.8%, p=0.09), or Montana's (62.6%, p=0.14) — those three states form a real "leading cluster" with Idaho. It IS statistically distinguishable from Arizona, Tennessee, Georgia, Washington, California, and states further down the list (p<0.05 in each case). So the honest answer is: Idaho is the best point estimate, and remains so after cost-of-living adjustment, but the top 3-4 states are close enough that a claim of a single, unambiguous winner overstates the precision of the underlying survey data.

Why 2014-2024, and what "income" and "cost of living" mean here

Window: Today is September 2026. The Census Bureau's American Community Survey (ACS) 1-Year estimates — the most current state-level median household income series — are published about a year behind, so 2024 is the latest available year (confirmed via data_coverage on census.acs1_income; 2025 has not been published, and 2020 was never released due to COVID data-collection disruptions). 2014-2024 is therefore the most recent genuine 10-year window the data supports, and it is a clean full-decade comparison rather than a 9- or 11-year one.

"Incomes up the most" = growth, not the highest income level. Idaho actually ranks near the middle of the pack in the LEVEL of income ($81,166 in 2024, below the U.S. median of $81,604) — its distinction is the rate of increase, which matters for the question as posed ("seen their incomes go up the most").

"Cost of living" — two different adjustments, and why both matter: (1) National inflation (BLS CPI-U) removes the effect of rising prices over TIME but assumes every state faces the same prices — it is a time adjustment, not a place adjustment, and because it is a single national number applied equally to every state's 2014 income, it mathematically cannot change the RANKING of states by growth rate (it only rescales every state's growth figure by the same constant, confirmed with the connector's adjust_inflation tool: the CPI-U deflator from 2014 to 2024 is 1.325, i.e. 32.5% cumulative inflation). (2) BEA's Regional Price Parities (RPP) is the federal government's actual cross-STATE cost-of-living index — it is the adjustment that can change the ranking, because different states' cost of living rose at different rates. We applied RPP (all-items, line_code=1) to both the 2014 and 2024 income figures and recomputed growth in cost-of-living-adjusted terms. This is the adjustment that answers "does the lead survive accounting for cost of living," and it is the one that matters for this question.

Results: nominal growth ranking

At the bottom: North Dakota (+31.9%), Wyoming (+32.4%), Alaska (+33.6%) grew the least, partly reflecting the 2014-16 collapse in oil/commodity prices that these energy-exposed states were still recovering from at the start of the window.

Results: after adjusting for each state's own cost of living (BEA RPP)

Dividing income by (RPP/100) in both 2014 and 2024, then recomputing growth, gives the ranking below. Idaho stays #1, and its margin over the states just behind it in the nominal ranking widens — because Oregon's, Florida's, and Arizona's cost of living all rose meaningfully faster than Idaho's over the decade (Oregon RPP 99.7→103.4; Florida RPP 100.9→103.4; Arizona RPP 97.9→100.7; vs. Idaho RPP 93.7→95.5, a much smaller increase). Tennessee and Montana — whose RPP actually FELL slightly over the decade (92.8→91.9 and 95.2→94.6) — jump ahead of Oregon once cost of living is accounted for.

So the answer to "does it still hold once you account for cost of living" is yes — Idaho is the point-estimate leader both nominally and cost-of-living-adjusted, and the cost-of-living adjustment actually strengthens rather than weakens its case relative to its two closest nominal rivals (Oregon and Florida).

How confident should we be in "Idaho, #1"? (significance testing)

ACS 1-year estimates are sample-based and carry published margins of error (90% CI). Using the delta method to propagate each state's income MOE into a standard error on its growth rate, and comparing each top-10 state's growth rate to Idaho's:

Conclusion: Idaho, Oregon, Florida, and Montana form a genuine statistical "leading pack" — none of the three challengers can be ruled out as the true fastest-growing state given sampling uncertainty. Idaho is the best point estimate and (unlike Oregon and Florida) keeps its rank under the cost-of-living adjustment too, which is why we name it as the answer — but a reader should treat "Idaho, specifically" as the most likely single answer rather than a certainty.

Context from outside research

An unrelated but corroborating data point: the University of Utah's Kem C. Gardner Policy Institute (April 2025 report, cited via Yahoo/Deseret News) found Utah's state GDP grew 64% cumulatively over the same roughly 10-year span — the fastest in the nation — though that is GDP, not household income, and it measures the LEVEL leader in cost-of-living-adjusted income ($98,336, #1 in the nation) rather than the GROWTH leader. In our data, Utah's household income growth (+58.7% nominal) is solid but well behind Idaho's; Utah's distinction is a high adjusted income LEVEL sustained by large households and high labor-force participation, not the fastest growth rate. This is a useful reminder that "income growth" and "cost-of-living-adjusted income level" are different questions with different answers — Idaho leads on growth, Utah leads on adjusted level.

Separately, the Urban Institute's 50-year (1970-2023) analysis (via Governing.com) found Utah had the largest REAL income gain over that much longer window (+80%), with California, Arizona, and Colorado also standing out — a different time horizon that naturally surfaces a different leader than our 10-year window. West Virginia was flagged as the one state with essentially no real income growth over 50 years; in our 10-year window it also finished near the bottom (nominal +48.1%, lowest along with North Dakota, Wyoming, and Alaska).

The Census Bureau's own 2024 ACS brief ("Household Income in States and Metropolitan Areas: 2024," published September 2025) confirms our raw 2024 figures exactly (Idaho $81,166 ± $1,340) and reports that median household income rose in 29 states between 2023 and 2024 alone (inflation-adjusted), with Massachusetts, New Jersey, and Maryland holding the highest income LEVELS nationally — again, a level ranking rather than a decade-growth ranking, and one where Idaho does not appear (Idaho's income level is close to but not statistically different from the U.S. median).

Methodology and data notes

• Income series: census.acs1_income (ACS 1-Year Estimates), state median household income, years 2014 and 2024, all 50 states + DC pulled, DC and Puerto Rico excluded from the ranking (DC is a city, not a state; Puerto Rico is a territory).
• Cost-of-living series: econ.regional_price_parities, BEA SARPP table, line_code=1 (all items), years 2014 and 2024. RPP = 100 is the national average; e.g. Idaho's 2024 RPP of 95.5 means Idaho's cost of living was 4.5% below the national average.
• National inflation check: adjust_inflation tool, CPI-U (BLS series CUUR0000SA0), 2014→2024 deflator = 1.325 (32.5% cumulative national inflation) — confirms that Idaho's 69.6% nominal income growth outpaced overall inflation by a wide margin even before any state-specific cost-of-living adjustment.
• Significance testing: delta-method standard errors on each state's growth rate, derived from each year's published 90% CI margin of error (MOE/1.645 = SE), compared via a two-sample z-test assuming independence across ACS survey years and states.
• Limitation: BEA RPP itself is not a sample-based survey estimate and this analysis did not have access to its own uncertainty bounds, so the cost-of-living-adjusted ranking is reported as a point-estimate re-ranking, not independently significance-tested.