(KRON) — It’s no secret that the Bay Area is one of the most expensive places to live in the entire United States. A recent study by SmartAsset shows four of the five wealthiest counties in the country are in the Bay Area — further showing the high cost of living in the Northern California region.

SmartAsset: 10 Wealthiest Counties in U.S.

Rank/CountyMedian IncomeInvestment IncomeMedian Home ValueOverall Wealth Index
1. San Mateo County, CA$136,837$149,818$1,495,191100.00
2. San Francisco, CA$126,187$134,035$1,272,79596.91
3. Santa Clara County, CA$140,258$90,292$1,468,20693.54
4. Marin County, CA$131,008$142,305$1,428,57891.68
5. Nantucket, MA$116,571$96,756$2,439,42888.02
6. New York County, NY$93,956$240,895$1,174,53080.90
7. Teton County, WY$94,498$437,754$1,624,08776.31
8. Falls Church City, VA$155,071$46,711$957,07572.89
9. Alameda County, CA$112,017$38,318$1,067,82372.07
10. Dukes County, MA$77,392$70,387$1,379,57668.61

SmartAsset used a county’s “overall wealth index” in its rankings — a score that measures a combination of three factors: median income, investment income and median home value.

Among the top five, third-ranked Santa Clara County has the highest median income ($140,258), according to the study. Only Falls Church City, VA ($155,071) had a higher median income in the overall top 10 list.

Check out SmartAsset’s interactive map and see the wealthiest counties in each state across the country. The map will show you where each county ranks both nationally and in its respective state.

Where other Bay Area counties ranked in U.S.

  • Contra Costa County: 18th
  • Napa County: 19th
  • Sonoma County: 22nd
  • Solano County: 69th

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To determine the wealthiest counties, SmartAsset measured three metrics: investment income, property value and per capita income.

“We started the analysis by calculating the Investment Index for each county by evenly weighing the Ordinary Dividends, Qualified Dividends, and Net Capital Gains. From there we calculated the Median Home Value, and the Per Capita Income for each county, and ranked them on all three metrics,” SmartAsset wrote.

SmartAsset used data from IRS SOI Tax Statistics, Zillow and the Bureau of Economic Analysis.