The drive from Decatur, IL to Mount Vernon, IL covers 122.4 miles and takes about 2h 28m behind the wheel.
This route is realistic as a one-day drive if you keep your stops efficient.
The route leans on South Business Route 51, I 57, 300 East Road for much of the mileage,
and the overall profile is mixed drive.
The longest uninterrupted segment is about 23.4 miles on South Business Route 51.
At current regular gas prices, budget about $19.14 one way before food or hotel costs.
Trip Pace
Same-day drive is realistic
A same-day return is realistic if you keep stops short.
Midpoint
61.2 miles from Decatur, IL
A natural place for your longest stop of the day
, about 1h 17m into the drive
.
Mixed drive route profile with national parks nearby.
Drive Character
The drive from Decatur, IL to Mount Vernon, IL covers 122.4 miles and takes about 2h 28m, using a mix of highways and local roads.
Expect a mix of faster highway mileage and slower local approaches near the beginning or end.
There are about 25 navigation steps in the underlying route data, so the final approach matters more than the middle miles.
South Business Route 51 is the longest continuous segment at about 23.4 miles.
How Hard Is This Drive?
This route mixes highway mileage with some local-road sections near the start or finish. There are only a few real navigation decisions along the way. The trickiest moment comes around 0.1 miles in near US 51 Business / South Main Street.
Driving Effort3/10
Easy - simple navigation with a manageable amount of wheel time
Balances navigation complexity with total wheel time.
This is a straightforward 2h 28m drive. You will face about 11 decision points, but nothing that requires special attention if you follow navigation.
Where does it get tricky?
The main spots that need attention: at 0.1 miles (US 51 Business / South Main Street): Navigation decision point; at 32.8 miles (US 51; IL 16 / North 2600 East Road): Navigation decision point; at 34.4 miles (US 51; IL 16 / East 1st Street): Navigation decision point.
Critical Maneuvers
5 of 11 key points
These are the spots where you need to pay the most attention. Preview them before you drive.
4
0.1 mi into trip|~0m in|US 51 Business / South Main Street
Turn left onto US 51 Business / South Main Street
Navigation decision point
4
32.8 mi into trip|~40m in|US 51; IL 16 / North 2600 East Road
Turn right onto US 51; IL 16 / North 2600 East Road
Navigation decision point
4
34.4 mi into trip|~44m in|US 51; IL 16 / East 1st Street
Turn right onto US 51; IL 16 / East 1st Street
Navigation decision point
4
65.5 mi into trip|~1h 22m in|US 40; US 51; IL 185 / West Gallatin Street
Turn left onto US 40; US 51; IL 185 / West Gallatin Street
Navigation decision point
5
119.3 mi into trip|~2h 22m in
Take the exit toward IL 15: Ashley, Mt. Vernon
Exit ramp - move to the correct lane early. Multiple destination signs - pick the right one
Toward IL 15: Ashley, Mt. Vernon
Main Roads
Road
Distance
Duration
South Business Route 51
23.4 mi
29m
I 57
21.4 mi
23m
300 East Road
15.1 mi
17m
United States Highway 51
13.4 mi
15m
County Road 875 East
11.1 mi
12m
250E
10.4 mi
11m
North 2600 East Rd
7.9 mi
9m
US 50
7.6 mi
8m
Longest stretch:
South Business Route 51
— 23.4 mi, about 29m
Turn-by-Turn Driving Directions
Step-by-step road directions between Decatur, IL and Mount Vernon, IL.
1
Start on East Wood Street
298 ft·15 sec·East Wood Street
2
Turn left onto US 51 Business
1.4 mi·2 min·South Main Street
3
Continue on US 51 Business
3.8 mi·5 min·South Business Route 51
4
Take the ramp onto US 51 Business
20 mi·23 min·South Business Route 51
5
Continue on US 51
7.9 mi·9 min·North 2600 East Rd
6
Turn right onto US 51; IL 16
1.0 mi·1 min·North 2600 East Road
7
Continue on US 51; IL 16
0.5 mi·1 min·Jackson Street
8
Turn left onto US 51; IL 16
467 ft·8 sec·Cedar Street
9
Turn right onto US 51; IL 16
0.4 mi·1 min·East 1st Street
10
Turn left onto US 51; IL 16
0.4 mi·29 sec·South Poplar Street
11
Turn straight onto US 51
0.6 mi·2 min·Fair Avenue
12
Continue on US 51
2.0 mi·2 min·County Road 2400 E
13
Continue on US 51
15 mi·17 min·300 East Road
14
Continue on US 51
11 mi·12 min·County Road 875 East
15
Continue on US 51
1.5 mi·1 min·North Kennedy Boulevard
16
Turn left onto US 40; US 51; IL 185
0.5 mi·34 sec·West Gallatin Street
17
Turn right
0.1 mi·7 sec
18
Continue on US 51
13 mi·15 min·United States Highway 51
19
Continue on US 51
10 mi·11 min·250E
20
Turn left onto US 50
7.6 mi·8 min·US 50
21
Take the exit
0.3 mi·45 sec
22
Merge onto I 57
21 mi·23 min·I 57
23
Take the exit
0.3 mi·41 sec
Toward IL 15: Ashley, Mt. Vernon
24
Turn straight onto IL 15
2.8 mi·5 min·Broadway Street
25
Arrive at destination
IL 15
Trip Plan
Morning Departure
Leave by 9 AM and you'll arrive before lunch.
Evening Departure
Even a 4 PM departure gets you there before dark in summer.
You can normally do this drive in one day.
You may only need one short stretch break if traffic stays light.
The halfway point lands around 61.2 miles from Decatur, IL, or about 1h 17m into the drive.
The longest continuous stretch on this route runs about 23.4 miles.
This is a comfortable same-day trip.
Departure
Before you leave
Start with fuel, water, and navigation already sorted so the first hour feels easy.
First stop
Around 27 miles or 34m in
Use this first pause for coffee, a restroom break, and a quick traffic check ahead.
Halfway reset
Around 61.2 miles or 1h 17m in
This is the best place for your longest stop, a real meal, and a full fuel check.
Final approach
Final hour starts around 2h 2m
Traffic, exits, and arrival timing usually matter more near Mount Vernon, IL than in the middle of the route.
Before You Leave
+
Open the route before leaving Decatur, IL so your first major turns are already loaded.
+
Leave with enough water and a charging cable within reach, not packed away.
+
Check your fuel range against the first long segment, especially if you are starting outside city service areas.
Day 1
Settle into the route from Decatur, IL
This is one driving day of about 122.4 miles and 2h 28m.
Your first comfortable stop window is around 27 miles from Decatur, IL.
This route can stay practical as a one-day drive if traffic stays reasonable.
The longest stretch is on South Business Route 51 for about 23.4 miles.
Where to Stop
Rest stops, refuel points, and overnight suggestions along this route.
Halfway Point
Midpoint
About 61.2 mi from Decatur, IL
· 1h 17m into the drive
Station data from NREL Alternative Fuel Stations database.
Driving Electric?
About $13 in charging
· 0 stops
· 67% less CO2
Vehicle Type
kWh
Stops
DC Fast
Home Charge
Average EV
36.7
0
$12.85
$5.88
Efficient EV
30.6
0
$10.71
$4.90
EV Truck/SUV
49
0
$17.14
$7.83
Gas CO2
43 kg
EV CO2
14 kg (67% less)
This trip is well within single-charge range for most EVs. No charging stops needed if you start fully charged.
DC fast charging avg $0.35/kWh. Home charging avg $0.16/kWh. US grid CO2: 0.39 kg/kWh.
Travel Intel
Current conditions at both ends of the drive.
Forecast as of Apr 15, 2026
Origin
Decatur, IL
Late night
in Decatur on Saturday
Local time
4:19 AM
CDT
Current temp
74°F
Unavailable
Live forecast
Destination
Mount Vernon, IL
Late night
in Mount Vernon on Saturday
Local time
4:19 AM
CDT
Current temp
56°F
Unavailable
Live forecast
54°F
Vandalia, IL
61 mi in
Seasonal Notes
Summer travel usually means heavier construction, hotter rest stops, and busier weekend traffic around major cities.
Winter travel shortens daylight, so a route that looks manageable on paper can feel much longer after dark.
Holiday weekends tend to make both departure and arrival windows slower than the raw route time suggests.
Time zone
Same local time
Origin and destination are on the same clock, so arrival timing is easier to judge at a glance.
Temperature spread
18 degrees cooler at arrival
A meaningful temperature swing is a good cue to rethink layers, water, and how soon you want to arrive.
Road read
2h 28m on the road
Use the two city cards together: check the sky where you start, then compare it with the local time and temperature at arrival.
Weather data from the National Weather Service. Conditions may change; check closer to your travel date.
Frequently Asked Questions
The drive from Decatur, IL to Mount Vernon, IL covers 122.4 miles and takes about 2h 28m without stops. Add 15-30 minutes for a fuel or rest stop on longer drives.
The main roads are South Business Route 51, I 57, 300 East Road. Expect a mix of highway and local road driving.
This is a comfortable same-day trip.
The midpoint is about 61.2 miles from Decatur, IL. Look for rest areas, gas stations, or food options near the halfway mark.
At current regular gas prices, expect to spend about $19.14 one way. This estimate uses 25.4 MPG — your actual cost will vary with your vehicle's fuel efficiency and current gas prices.
Leave by 9 AM and you'll arrive before lunch. Even a 4 PM departure gets you there before dark in summer.
This is a straightforward 2h 28m drive. You will face about 11 decision points, but nothing that requires special attention if you follow navigation.
The main spots that need attention: at 0.1 miles (US 51 Business / South Main Street): Navigation decision point; at 32.8 miles (US 51; IL 16 / North 2600 East Road): Navigation decision point; at 34.4 miles (US 51; IL 16 / East 1st Street): Navigation decision point.
The route from Decatur, IL to Mount Vernon, IL does not surface many named destination signs beyond the main corridor.
How this page is built
Compiled by the Trip.ovh planning team at COD Solutions Oy from open government datasets — OSRM over OpenStreetMap for geometry, EIA for fuel prices, NREL for EV charging, and NPS for national parks. See our methodology for refresh cadence and limitations.
