A healthy regional economy and strong real estate market could not prevent 3.5% of Riverside County mortgages from being labeled “seriously underwater” at year’s end in a recent study.

Attom Data Solutions says Riverside County had 16,040 underwater homes in last year’s fourth quarter. Attom tracked what it sees as some of the most troublesome home loans: mortgages that are 25% greater (or more) than the value of the home. While this may sound like a lot of troubled loans, Riverside County’s share of seriously underwater mortgages is middle-of-the-pack: It ranked 23rd lowest among the 50 most-populated U.S. counties.

Underwater loans are seen as being at a high risk of default. If the economy sours or if the owner’s finances get stretched, there’s little financial motivation keeping the borrower in these homes. Challenges that “underwater” stats highlight are lingering value issues from the bubble bursting a decade ago as well as more recently reduced values of high-end housing.

California had 189,896 seriously underwater home loans in the fourth quarter. That’s 2.7% of all mortgaged properties, third-lowest nationwide. By the way, 7% of mortgages in the rest of the U.S. are seriously underwater by Attom’s math.

If you look at the Riverside County results at the neighborhood level, the desert resort towns had higher levels of underwater homes while bedroom communities closer to the coast had fewer. Look at the number and share of seriously underwater mortgages in major Riverside County ZIP codes and how that percentage ranked among 979 California ZIPs tracked by Attom.

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The 10 Riverside County ZIPs with the highest share of “seriously” underwater mortgages …

1. Indian Wells 92210: 216 or 9.38% — No. 968 statewide.

2. Palm Desert 92211: 796 or 7.90% — No. 962 statewide.

3. Rancho Mirage 92270: 514 or 7.59% — No. 957 statewide.

4. Blythe 92225: 158 or 7.24% — No. 955 statewide.

5. Banning 92220: 399 or 6.39% — No. 937 statewide.

6. La Quinta 92253: 868 or 6.23% — No. 928 statewide.

7. Palm Desert 92260: 467 or 6.05% — No. 919 statewide.

8. Sun City 92586: 346 or 5.64% — No. 906 statewide.

9. Desert Hot Springs 92240: 351 or 5.32% — No. 890 statewide.

10. Indio 92203: 412 or 5.14% — No. 883 statewide.

The 10 ZIPs with the lowest shares ….

45. Murrieta 92563: 344 or 2.28% — No. 488 statewide.

46. Perris 92571: 214 or 2.20% — No. 459 statewide.

47. Mira Loma 91752: 129 or 2.18% — No. 446 statewide.

48. Temecula 92591: 189 or 2.15% — No. 435 statewide.

49. Winchester 92596: 133 or 2.14% — No. 433 statewide.

50. Moreno Valley 92551: 130 or 2.13% — No. 427 statewide.

51. Riverside 92503: 333 or 2.10% — No. 419 statewide.

52. Corona 92882: 264 or 1.99% — No. 383 statewide.

53. Riverside 92501: 57 or 1.78% — No. 314 statewide.

54. Riverside 92505: 115 or 1.59% — No. 249 statewide.

And the rest …

11. Sun City 92587: 237 or 5.14% — No. 882 statewide.

12. Hemet 92545: 342 or 4.26% — No. 831 statewide.

13. Indio 92201: 439 or 4.19% — No. 830 statewide.

14. Hemet 92543: 169 or 4.18% — No. 829 statewide.

15. Corona 92880: 652 or 4.00% — No. 816 statewide.

16. Hemet 92544: 329 or 3.92% — No. 811 statewide.

17. Norco 92860: 214 or 3.71% — No. 793 statewide.

18. Murrieta 92562: 515 or 3.64% — No. 790 statewide.

19. Beaumont 92223: 444 or 3.59% — No. 783 statewide.

20. Corona 92883: 290 or 3.59% — No. 781 statewide.

21. Palm Springs 92264: 244 or 3.57% — No. 778 statewide.

22. Palm Springs 92262: 306 or 3.42% — No. 753 statewide.

23. Cathedral City 92234: 329 or 3.21% — No. 717 statewide.

24. Perris 92570: 189 or 3.17% — No. 709 statewide.

25. Wildomar 92595: 182 or 3.11% — No. 701 statewide.

26. Sun City 92585: 155 or 3.11% — No. 700 statewide.

27. San Jacinto 92583: 163 or 3.11% — No. 699 statewide.

28. Corona 92881: 220 or 3.11% — No. 698 statewide.

29. Moreno Valley 92555: 274 or 3.07% — No. 684 statewide.

30. Idyllwild 92549: 64 or 3.02% — No. 671 statewide.

31. Lake Elsinore 92530: 283 or 2.82% — No. 637 statewide.

32. Menifee 92584: 322 or 2.75% — No. 628 statewide.

33. Moreno Valley 92557: 295 or 2.67% — No. 604 statewide.

34. Riverside 92506: 313 or 2.65% — No. 601 statewide.

35. Corona 92879: 217 or 2.62% — No. 590 statewide.

36. Riverside 92507: 161 or 2.48% — No. 560 statewide.

37. Riverside 92508: 200 or 2.46% — No. 556 statewide.

38. Riverside 92504: 246 or 2.46% — No. 554 statewide.

39. Temecula 92592: 461 or 2.44% — No. 542 statewide.

40. San Jacinto 92582: 88 or 2.40% — No. 531 statewide.

41. Riverside 92509: 305 or 2.40% — No. 530 statewide.

42. Lake Elsinore 92532: 132 or 2.37% — No. 520 statewide.

43. Moreno Valley 92553: 265 or 2.36% — No. 518 statewide.

44. Coachella 92236: 131 or 2.35% — No. 514 statewide.