U.S. Frost Dates by Weather Station

NOAA station USC00114108 · Illinois

Frost Dates for Hillsboro, IL

NOAA weather station Hillsboro (USC00114108), Illinois · elevation 630 ft (192 m) · hardiness zone 6b*

  • Lower-risk planting dateafter April 28only 1 spring in 10 still has a frost later
  • Typical last frostApril 1350% chance of a frost after it
  • Typical first fall frostOctober 2450% chance of a frost before it
  • Frost-free season192 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Hillsboro, ILSpring: a frost after March 30 in 9 years out of 10, after April 13 in half of the years, after April 28 in 1 year out of 10. Fall: the first frost comes before October 10 in 1 year out of 10, before October 24 in half of the years, before November 4 in 9 years out of 10. Typical frost-free season: 192 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 13First frost ~Oct 24Frost season at Hillsboro, ILSpring: a frost after March 30 in 9 years out of 10, after April 13 in half of the years, after April 28 in 1 year out of 10. Fall: the first frost comes before October 10 in 1 year out of 10, before October 24 in half of the years, before November 4 in 9 years out of 10. Typical frost-free season: 192 days.JFMAMJJASONDLast frost ~Apr 13First frost ~Oct 24
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.Today

Frost dates (32°F)

Probability of frost, based on 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 28October 10
50% (typical)April 13October 24
90% (likely)March 30November 4
Frost-free season (32°F, 50% chance)
192 days
Hard frost (28°F), last in spring, 50% chance after
April 2
Hard frost (28°F), first in fall, 50% chance before
November 2

The last 15 years (2006–2020 normals)

Typical last frost April 13 (same as the 30-year normal), typical first fall frost October 24. Frost-free season 192 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Hillsboro: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 28, 20% April 23, 30% April 19, 40% April 17, 50% April 13, 60% April 10, 70% April 7, 80% April 4, 90% March 30. Observed last spring frost in recent years: 2021 April 21, 2022 April 19, 2025 April 12, 2026 March 29.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 28Apr 13Mar 302021: April 212022: April 192025: April 122026: March 29Fall at Hillsboro: chance of a frost before this dateFall, chance of a frost before the date: 10% October 10, 20% October 15, 30% October 18, 40% October 21, 50% October 24, 60% October 26, 70% October 29, 80% October 31, 90% November 4. Observed first fall frost in recent years: 2021 November 3, 2022 October 18, 2024 October 16, 2025 November 2.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 10Oct 24Nov 42021: November 32022: October 182024: October 162025: November 2
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021April 21November 3
2022April 19October 18
2023incomplete recordincomplete record
2024incomplete recordOctober 16
2025April 12November 2
2026March 29season not over yet

What these dates mean

October 10 marks the cautious fall date for finishing the harvest of tender crops in Hillsboro, because there is only a 10 % chance that a light frost has occurred earlier. In the spring the comparable cautious date is April 28, when the chance of a light frost later in the season is 10 %.

For a gardener the 50 % dates are reference points: April 13 and October 24 are the median dates for light frost, meaning there is an even chance of a frost occurring on either side of each date. The hard-frost median dates are April 2 in spring and November 2 in fall; a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F. The early-spring date of March 30 carries a 90 % chance of a light frost later, while November 4 carries a 90 % chance of a light frost earlier, both representing higher-risk choices for tender crops.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after April 28" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before October 10" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Hillsboro, ILNumbered nearest stations: 1 — Ramsey, IL — 21 mi; 2 — near Carlyle, IL — 38 mi; 3 — Jerseyville, IL — 46 mi; 4 — Salem, IL — 46 mi; 5 — Effingham, IL — 47 mi.ILMO25 mi · 40 km1. Ramsey, IL — 21 mi12. near Carlyle, IL — 38 mi23. Jerseyville, IL — 46 mi34. Salem, IL — 46 mi45. Effingham, IL — 47 mi5
  1. Ramsey, IL 21 mi (34 km)
  2. near Carlyle, IL 38 mi (61 km)
  3. Jerseyville, IL 46 mi (74 km)
  4. Salem, IL 46 mi (75 km)
  5. Effingham, IL 47 mi (75 km)

Sources

* Hardiness zone 6b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 39.1611, -89.4919.