How far is Castlewood, CO from Boulder, CO?
The driving distance from Castlewood, CO to Boulder, CO is about 42.9 miles (69.1 km), with a travel time of about 00h 54m by car.
- The straight-line flight distance is about 35.6 miles (57.3 km).
- For a round trip, plan for roughly 01h 48m of driving time before adding stops, traffic, or weather delays.
- A comfortable departure window is usually 8:00 AM to 10:00 AM MDT.
Reverse, save, or send this route
This route works well as a day trip with time at the destination. Copy the route link, send it to another device, or print a clean version before you head out.
This route works well as a day trip with time at the destination.
Flight Distance
Driving Distance
Gas Cost Calculator
Leave and Arrive Planner
Pick a departure time to see your estimated arrival and same-day return window.
Drive time stays fixed at 00h 54m.
A morning start gives you useful time at the destination and keeps the return out of the late evening.
You are leaving earlier than the recommended window, which gives you extra margin for breaks and traffic.
Halfway Point
A useful midpoint for breaks, coffee, or meeting in the middle.
City in Freeborn County, Minnesota, United States of America
Route Weather Snapshot
Check the forecast at both ends before you head out.
Sunny
Sunny
Driving Route Map
The map below follows the saved road route between Castlewood and Boulder.
Turn-by-Turn Driving Directions
Step-by-step road directions between Castlewood and Boulder.
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1
Start on East Fremont Drive
704 ft · 33 sec · East Fremont Drive
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2
Turn right onto East Hinsdale Avenue
151 m · 24 sec · East Hinsdale Avenue
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3
At the end of the road, turn right onto South Quebec Street
1.3 km · 2 min · South Quebec Street
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4
Turn right onto East Arapahoe Road
1.1 mi · 2 min · East Arapahoe Road
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5
Take the ramp straight toward I 25 North: Denver
859 ft · 23 sec
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6
Merge slight left onto South Valley Highway
19.5 mi · 25 min · South Valley Highway
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7
Take the exit slight left toward US 36 West: Westminster, Boulder
2930 ft · 52 sec
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8
Merge slight right onto Denver–Boulder Turnpike
2.1 mi · 2 min · Denver–Boulder Turnpike
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9
Keep slight right to continue on Denver–Boulder Turnpike
1.7 mi · 2 min · Denver–Boulder Turnpike
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10
Keep slight right to continue on Denver–Boulder Turnpike
2.3 mi · 3 min · Denver–Boulder Turnpike
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11
Keep slight right to continue on Denver–Boulder Turnpike
1.9 mi · 2 min · Denver–Boulder Turnpike
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12
Keep slight right to continue on Denver–Boulder Turnpike
2.1 mi · 2 min · Denver–Boulder Turnpike
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13
Keep slight right to continue on Denver–Boulder Turnpike
2.9 mi · 3 min · Denver–Boulder Turnpike
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14
Keep slight right to continue on Denver–Boulder Turnpike
2.4 mi · 3 min · Denver–Boulder Turnpike
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15
Keep slight right to continue on Denver–Boulder Turnpike
2.2 mi · 3 min · Denver–Boulder Turnpike
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16
Keep slight left to continue on Denver–Boulder Turnpike
2.3 mi · 3 min · Denver–Boulder Turnpike
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17
Continue on 28th Street
1.2 km · 2 min · 28th Street
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18
Turn left onto Arapahoe Avenue
1 km · 2 min · Arapahoe Avenue
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19
Turn right onto 19th Street
44 m · 11 sec · 19th Street
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20
Turn left
27 m · 5 sec
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21
Arrive at your destination
0 m · 1 sec
Car Route Details
A richer read on the saved driving route between Castlewood and Boulder.
Highway-focused drive
Most of the mileage stays on named highways, so the important moments are ramps, exits, merges, and the final local approach.
South Valley Highway
Merge slight left onto South Valley Highway
19.5 mi · 00h 25m
Route Summary
A quick read on whether this route feels easy, ambitious, or worth planning around.
A comfortable day-trip route
This route works well as a day trip. You can leave in the morning, spend meaningful time at the destination, and still return the same day.
Sunny leaving Castlewood and Sunny near Boulder.
Trip Questions
Direct answers travelers usually want before committing to the drive.
How long does it take to drive from Castlewood to Boulder?
The road trip is about 42.9 miles (69.1 km) and usually takes 00h 54m in normal driving conditions.
Is this a same-day trip or an overnight route?
This route works well as a day trip. You can leave in the morning, spend meaningful time at the destination, and still return the same day.
What is the halfway point on this route?
Twin Lakes is a useful midpoint, sitting about 21.7 miles from Castlewood and 21.2 miles from Boulder.
How much longer is the road route than the straight-line distance?
The direct path is about 35.6 miles (57.3 km), while the road route adds roughly 7.3 extra miles because roads do not follow the straight air line.
When is the best time to leave for this route?
A good departure window is usually 8:00 AM to 10:00 AM MDT. If you want a more comfortable same-day return, try to leave by 4:42 PM MDT.
How much will gas cost for this route?
Using about 28.3 MPG, regular gas is estimated at $5.62 one way or $11.24 round trip. Estimated CO2 is about 13.5 kg one way.
What should you check before leaving?
Before you leave, expect Sunny around Castlewood and Sunny near Boulder.
Stop Ideas Near Twin Lakes
Useful break, food, and waypoint ideas within about 15 miles of the route midpoint.
Fairplay Park
Denver City Council
Town Hall Arts Center
Municipal Court Park
Transit and Meeting Points
Useful pickup, handoff, or rendezvous points close to Twin Lakes.
Denver (Bus Station), Colorado
Union Station
Boulder, Colorado
Longmont, Colorado
Flight Path Map
This map shows the direct air route between Castlewood and Boulder. Straight-line distance: 35.62 mi (57.32 km).
#1 Castlewood
City in Hamlin County, South Dakota, United States
| Population | 25,271 |
| Coordinates | 39.5847100, -104.9010900 |
| Altitude | 1746 |
| Country | United States |
#2 Boulder
The most populous city in Boulder County, Colorado.
| Population | 107,645 |
| Coordinates | 40.0149900, -105.2705500 |
| Altitude | 1624 |
| Country | United States |
End: (-105.27055, 40.014996)
Estimated Travel Time
Distance: 69 km by road
| Speed | Time |
|---|---|
| 30 mph (48.3 km/h) | 01h 25m |
| 40 mph (64.37 km/h) | 01h 04m |
| 50 mph (80.47 km/h) | 00h 51m |
| 60 mph (96.56 km/h) | 00h 42m |
| 70 mph (112.65 km/h) | 00h 36m |
| 80 mph (129 km/h) | 00h 32m |
Fuel, Round Trip and CO2
Estimated fuel cost and emissions for this route.
| Fuel | $/gal | One way | Round trip |
|---|---|---|---|
| Regular gas | $3.70 | $5.62 | $11.24 |
| Mid-grade | $4.08 | $6.21 | $12.42 |
| Premium | $4.39 | $6.67 | $13.35 |
| Diesel | $4.74 | $7.20 | $14.40 |
Assumes 8.3 L/100 km (about 28.3 MPG). CO2 is an estimate and varies by vehicle, fuel blend, traffic, and terrain.
Prices in Colorado · Apr 16, 2026
Distance to Other Cities
Planning a road trip? See the full trip guide on Trip.ovh — stops, fuel costs, weather, and departure timing.