These are the largest U.S. counties with the greatest housing risks

While the country grapples with an affordability crisis, some regions are more at risk than others. Among the counties with more than 1 million residents, a cluster of residential markets in California, Pennsylvania and Illinois has surfaced as the nation’s most vulnerable.

Riverside County, California, leads the list as the riskiest highly populated county in the United States, though it ranks 29th nationwide, according to an analysis from data provider Attom. To determine the riskiest counties for housing in the country, Attom looked at foreclosure activity, unemployment rates, home affordability and share of properties “underwater,” meaning homeowners’ mortgages are at least 25 percent more than the market value of their homes, in counties with enough data to analyze.

The Inland Empire hub, which has about 2.4 million residents, faces a dual threat: homeowners must spend nearly 66 percent of their average local wages to cover homebuying expenses, as the median home in the fourth quarter cost $600,000, almost double the national figure. Meanwhile, foreclosure filings affected one in every 811 properties in the fourth quarter, also almost double the national figure.

Neighboring San Bernardino County (fourth among top counties, 49th overall) mirrors this instability, with one of every 777 properties with a foreclosure filing, and homeowners needing to shell out more than 54 percent of their wages to cover the costs of buying a property.

These markets, along with Fresno and Contra Costa Counties in California, which also cracked the top 10 riskiest housing markets among the most populous areas in the country, had fourth-quarter unemployment rates well above the national average of 4.5 percent. Fresno’s was the highest, at 8.2 percent.

The affordability crisis in California has long been troubling and starker than national figures. Nationwide, a homeowner needs to spend just under a third of their income to buy a house, and one in every 1,274 homes is in some state of foreclosure, per Attom’s analysis. Roughly 56 percent of the 595 counties Attom analyzed require homeowners to cough up more than a third of their wages.

Housing markets beyond the West Coast also had red flags. For instance, Philadelphia County in Pennsylvania presents a different type of risk profile. While it remains relatively affordable — requiring just 19 percent of average income to buy a home there — it suffers from the highest underwater rate among populous counties. More than 8 percent of Philadelphia homeowners owe more on their mortgages than their homes are worth, a precarious position as the foreclosure rate in the fourth quarter was 0.22 percent, more than triple the national rate.

Cook County, Illinois, is in a similar position. Buyers there need to cough up roughly a quarter of their income to purchase a typical home. But 5.5 percent of its homes are underwater, second to Philadelphia among the most populous counties.

Both Cook and Philadelphia Counties were the only top-10 most populous counties whose median sale prices in the fourth quarter were below the national figure of about $365,000. In Philadelphia, the median price was about $239,000; in Cook County, it was $318,000.