How far is Boulder, CO from Castlewood, CO?
The driving distance from Boulder, CO to Castlewood, CO is about 42.4 miles (68.3 km), with a travel time of about 00h 56m by car.
- The straight-line flight distance is about 35.6 miles (57.3 km).
- For a round trip, plan for roughly 01h 53m 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 56m.
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.
Mostly Sunny
Mostly Sunny
Driving Route Map
The map below follows the saved road route between Boulder and Castlewood.
Turn-by-Turn Driving Directions
Step-by-step road directions between Boulder and Castlewood.
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1
Start on the route
27 m · 7 sec
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2
Turn right onto 19th Street
44 m · 14 sec · 19th Street
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3
Turn left onto Arapahoe Avenue
3210 ft · 2 min · Arapahoe Avenue
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4
Turn right onto 28th Street
1.2 km · 2 min · 28th Street
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5
Turn straight onto Denver–Boulder Turnpike
3.4 mi · 4 min · Denver–Boulder Turnpike
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6
Keep slight right to continue on Denver–Boulder Turnpike
1.7 mi · 2 min · Denver–Boulder Turnpike
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7
Keep slight right to continue on Denver–Boulder Turnpike
2.6 mi · 3 min · Denver–Boulder Turnpike
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8
Keep slight right to continue on Denver–Boulder Turnpike
2.4 mi · 3 min · Denver–Boulder Turnpike
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9
Keep slight right to continue on Denver–Boulder Turnpike
2.2 mi · 3 min · Denver–Boulder Turnpike
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10
Keep slight right to continue on Denver–Boulder Turnpike
1.9 mi · 2 min · Denver–Boulder Turnpike
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11
Keep slight right to continue on Denver–Boulder Turnpike
2.5 mi · 3 min · Denver–Boulder Turnpike
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12
Keep slight right to continue on Denver–Boulder Turnpike
2 mi · 2 min · Denver–Boulder Turnpike
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13
Keep slight right to continue on Denver–Boulder Turnpike
1.1 mi · 1 min · Denver–Boulder Turnpike
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14
Take the exit slight right toward I 25 south: Denver
2497 ft · 47 sec
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15
Continue on I 25 south: Denver
2037 ft · 34 sec
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16
Merge slight left onto North Valley Highway
18.8 mi · 24 min · North Valley Highway
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17
Take the exit slight right toward CO 88: Arapahoe Road
1289 ft · 29 sec
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18
Turn right onto East Arapahoe Road
2024 ft · 46 sec · East Arapahoe Road
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19
Turn left onto South Uinta Street
1.1 km · 2 min · South Uinta Street
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20
At the end of the road, turn right onto South Tamarac Court
593 ft · 28 sec · South Tamarac Court
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21
Turn right onto East Fremont Avenue
1294 ft · 57 sec · East Fremont Avenue
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22
Arrive at your destination
0 m · 1 sec · East Fremont Drive
Car Route Details
A richer read on the saved driving route between Boulder and Castlewood.
Highway-focused drive
Most of the mileage stays on named highways, so the important moments are ramps, exits, merges, and the final local approach.
North Valley Highway
Merge slight left onto North Valley Highway
18.8 mi · 00h 24m
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.
Mostly Sunny leaving Boulder and Mostly Sunny near Castlewood.
Trip Questions
Direct answers travelers usually want before committing to the drive.
How long does it take to drive from Boulder to Castlewood?
The road trip is about 42.4 miles (68.3 km) and usually takes 00h 56m 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 21.2 miles from Boulder and 21.2 miles from Castlewood.
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 6.8 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 4:36 PM MDT.
How much will gas cost for this route?
Using about 28.3 MPG, regular gas is estimated at $5.55 one way or $11.09 round trip. Estimated CO2 is about 13.3 kg one way.
What should you check before leaving?
Before you leave, expect Mostly Sunny around Boulder and Mostly Sunny near Castlewood.
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 Boulder and Castlewood. Straight-line distance: 35.62 mi (57.32 km).
#1 Boulder
The most populous city in Boulder County, Colorado.
| Population | 107,645 |
| Coordinates | 40.0149900, -105.2705500 |
| Altitude | 1624 |
| Country | United States |
#2 Castlewood
City in Hamlin County, South Dakota, United States
| Population | 25,271 |
| Coordinates | 39.5847100, -104.9010900 |
| Altitude | 1746 |
| Country | United States |
End: Castlewood (-104.90109, 39.58471)
Estimated Travel Time
Distance: 68 km by road
| Speed | Time |
|---|---|
| 30 mph (48.3 km/h) | 01h 24m |
| 40 mph (64.37 km/h) | 01h 03m |
| 50 mph (80.47 km/h) | 00h 50m |
| 60 mph (96.56 km/h) | 00h 42m |
| 70 mph (112.65 km/h) | 00h 36m |
| 80 mph (129 km/h) | 00h 31m |
Fuel, Round Trip and CO2
Estimated fuel cost and emissions for this route.
| Fuel | $/gal | One way | Round trip |
|---|---|---|---|
| Regular gas | $3.70 | $5.55 | $11.09 |
| Mid-grade | $4.08 | $6.13 | $12.25 |
| Premium | $4.39 | $6.59 | $13.17 |
| Diesel | $4.74 | $7.11 | $14.21 |
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.