S
M
T
W
T
F
S
30
84°
62°
31
81°
60°
1
79°
63°
2
80°
62°
3
85°
63°
4
85°
63°
5
80°
61°
6
80°
60°
7
85°
59°
8
83°
55°
9
82°
54°
10
79°
58°
11
79°
54°
12
83°
54°
13
83°
60°
14
82°
54°
15
80°
52°
16
75°
53°
17
76°
52°
18
78°
55°
19
82°
52°
20
81°
55°
21
81°
57°
22
82°
56°
23
81°
52°
24
79°
50°
25
80°
49°
26
79°
55°
27
80°
55°
28
79°
54°
29
80°
54°
30
79°
52°
1
76°
54°
2
78°
54°
3
79°
52°
Temperature Graph
°F
Avg. Hi
Avg. Lo
Actual Hi
Actual Lo
Forecast Hi
Forecast Lo
September Weather in Collinsville
Collinsville's September 2026 forecast shows daily high temperatures ranging from 75° to 85°, with overnight lows between 49° and 63°. The average high for September is 80° with an average low of 56°. AccuWeather's monthly forecast extends further ahead than any other source, with day-by-day RealFeel® Temperatures giving a complete picture of how September weather will actually feel in Collinsville. See also: October | November | December.
