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Zillow Home Value Index, Zillow Home Value Index, bottom tier and Zillow Observed Rent Index, and every figure derived from them, reports included.

Visual story

The hottest counties

Each line is a county: on the left, how many days a summer its average high passed 90°F from 1951 to 1980; on the right, from 1996 to 2025. Every line climbs, by 6.6 days on average. Mercer is now the hottest, 22 days a summer; Sussex the coolest. Green lines are counties whose homes stand under more tree canopy than the typical county’s.

More shade than the typical countyLess

Atlantic: 7.8 → 14.8 daysAtlantic 815 AtlanticBergen: 11.5 → 16.8 daysBergen 1217 BergenBurlington: 13.7 → 21.7 daysBurlington 1422 BurlingtonCamden: 14.7 → 22.1 daysCamden 1522 CamdenCape May: 4.8 → 10.8 daysCape May 511 Cape MayCumberland: 8.7 → 16.9 daysCumberland 917 CumberlandEssex: 11.2 → 18.5 daysEssex 1119 EssexGloucester: 14.0 → 21.2 daysGloucester 1421 GloucesterHudson: 10.5 → 18.2 daysHudson 1118 HudsonHunterdon: 8.3 → 13.8 daysHunterdon 814 HunterdonMercer: 13.2 → 22.4 daysMercer 1322 MercerMiddlesex: 13.7 → 22.2 daysMiddlesex 1422 MiddlesexMonmouth: 10.6 → 18.9 daysMonmouth 1119 MonmouthMorris: 5.9 → 9.9 daysMorris 610 MorrisOcean: 8.4 → 16.3 daysOcean 816 OceanPassaic: 5.5 → 10.0 daysPassaic 510 PassaicSalem: 12.4 → 19.4 daysSalem 1219 SalemSomerset: 12.7 → 19.5 daysSomerset 1320 SomersetSussex: 4.5 → 6.8 daysSussex 57 SussexUnion: 12.7 → 20.3 daysUnion 1320 UnionWarren: 6.3 → 9.3 daysWarren 69 Warren

NOAA’s nClimGrid-Daily maximum temperature, gridded from weather stations and averaged over each county’s area, May to September; a day counts when the county average reached 90°F (32.2°C). A county average runs cooler than its hottest paved blocks, so these are a floor on how often a town felt it. Shade: tree canopy at the county’s homes, from the Forest Service’s canopy map; a county’s canopy is today’s, set beside its heat, not shown to cause it. More visual stories →