Freeport weather in September

In September, Freeport sees average daytime highs of 73°F and overnight lows near 54°F, with 3.6 in of rain across 8.8 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 78°F in the first days to 68°F by the end. The sky is clear or mostly clear about 42% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Freeport's 1st-clearest and 9th-windiest month. For the whole year in context, see Freeport's year-round climate.

Daytime high
73°
4th warmest
Overnight low
54°
9th coldest
Rainfall
3.6 in
8.8 wet days
Daylight
12 h 18 min
5:44 AM – 6:01 PM
Cloud cover
50%
1st clearest
Wind
7 mph
9th windiest
Solar energy
4.44 kWh/m²
Travel score
7.0
out of 10

Freeport is city and county seat and largest city of Stephenson County, Illinois, United States.

Density
802/km²
people per km²
Founded
1827

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 78°F in the first days to 68°F by the end.

A typical September day in Freeport reaches about 73°F in the afternoon and slips back to 54°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 62°F and 83°F. Set against its neighbours, September runs about 7°F cooler than August and about 13°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
17859
27859
37859
47858
57758
67758
77657
87657
97656
107656
117556
127555
137455
147455
157454
167354
177353
187253
197253
207252
217152
227151
237051
247050
256950
266950
276949
286849
296848
306748

How September really feels in Freeport

Once humidity and wind are folded in, September averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Freeport weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan29° / 15°1.87.55.89.30.0
Feb33° / 18°1.86.65.110.30.0
Mar46° / 29°2.69.52.911.61.2
Apr58° / 39°4.311.91.113.14.0
May69° / 50°4.413.1014.45.9
Jun79° / 60°4.3120156.3
Jul82° / 64°3.610.4014.86.4
Aug80° / 62°3.79.9013.76.7
Sep73° / 54°3.68.8012.37.0
Oct60° / 42°2.98.80.210.85.0
Nov46° / 31°2.47.81.79.61.3
Dec34° / 21°2.17.64.690.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 44%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15842
25842
35842
45941
55941
65941
75941
85941
95941
105941
115842
125842
135743
145743
155644
165644
175545
185545
195446
205446
215446
225446
235446
245248
255248
265248
275248
285248
295248
305248

Chance of precipitation in September

Any precipitation

Freeport gets around 3.6 in of rain over 8.8 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 30% and peaks near 31% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
229
329
429
529
628
728
828
929
1029
1129
1230
1330
1431
1531
1631
1731
1831
1931
2031
2131
2231
2331
2430
2530
2630
2729
2829
2928
3027

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 53% of days. Sticky, muggy-or-worse air turns up on roughly 12% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1272721187
2292721186
3302720176
4322720165
5342719154
6362719144
7382718143
8402718133
9412617133
10432617122
11452516122
12462516122
13482415111
14502415111
15522314101
16532214101
1755221391
1856211391
1959201281
2062191180
2163191170
2266181060
236817960
247016950
257115950
267414840
277414840
287513840
297812730
307812730

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207light breeze
217light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:28 AM to 6:00 AM, and sunset from 6:28 PM to 5:36 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:286:28
213.05:296:27
312.95:306:25
412.95:316:23
512.85:326:21
612.85:336:19
712.75:356:18
812.75:366:16
912.65:376:14
1012.65:386:12
1112.55:396:10
1212.55:406:09
1312.45:416:07
1412.45:426:05
1512.35:436:03
1612.35:446:01
1712.25:455:59
1812.25:475:58
1912.15:485:56
2012.15:495:54
2112.05:505:52
2212.05:515:50
2311.95:525:48
2411.95:535:47
2511.85:545:45
2611.85:555:43
2711.75:575:41
2811.75:585:39
2911.65:595:37
3011.66:005:36

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.44 kWh/m².

For context, solar energy here swings from a low near 1.66 kWh/m² to a high of 6.32 kWh/m² in June across the year — September's 4.44 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
15.0Bright
25.0Bright
34.9Bright
44.9Bright
54.9Bright
64.8Bright
74.8Bright
84.7Bright
94.7Bright
104.7Bright
114.6Bright
124.6Bright
134.5Bright
144.5Bright
154.4Bright
164.4Bright
174.3Bright
184.3Bright
194.3Bright
204.2Bright
214.2Bright
224.1Bright
234.1Bright
244.0Bright
254.0Bright
264.0Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Freeport?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

7.0
Sightseeing
1st-best month of the year
5.2
Beach & pool
4th-best month of the year

September is one of the better times to visit Freeport for general sightseeing.

What to pack for Freeport in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Freeport sees daytime highs around 73°F and nights near 54°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Freeport in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Freeport peaks around June 19 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 2 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 19UV 9Dec 22UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar4Moderate
Apr6High
May8Very high
Jun9Very high
Jul8Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov2Moderate
Dec2Low

Air quality in Freeport in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Freeport is worst in July — around 16 µg/m³ PM2.5 (moderate), about 2.0× the cleanest month (October, 8 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateModerateGoodJul 1915 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb13Moderate
Mar13Moderate
Apr12Good
May13Moderate
Jun14Moderate
Jul16Moderate
Aug14Moderate
Sep11Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Freeport?

Freeport sits at 42.3°N, 89.6°W, 778 ft above sea level, in United States. The nearest listed city is Rockford, 27 mi away.

Topography around Freeport

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Freeport.

Within 2 miles, the terrain around Freeport has only modest variations in elevation — a maximum elevation change of 177 ft around an average of 797 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 472 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 853 ft.

The land around Freeport is covered by trees (33%), grassland (24%) and cropland (21%) within 2 miles, cropland (75%) within 10 miles, and cropland (67%) within 50 miles.

2 miles
177 ft
10 miles
472 ft
50 miles
853 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Rockford 27 mi · Loves Park 29 mi · Machesney Park 30 mi · Dixon 32 mi · Beloit 34 mi · Sterling 35 mi · Belvidere 40 mi · Janesville 40 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Freeport (42.2967°, -89.6212°, elevation 778 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).