Spearfish to Watertown is 451.1 miles and takes about 7h 40m via I 90 and SD Highway 25, with a fuel budget near $69 and enough daylight to finish in a day. This route traverses the vast Great Plains region of South Dakota, offering a straightforward path across the state. Most of your travel will be on major highways, making it a practical choice for efficient transit. If you're looking to cover a significant distance within the state without extensive detours, this trip is designed for that purpose. Consider this a solid option for a single-day drive where the focus is on reaching your destination.
Trip Pace
Same-day drive is realistic
A same-day return is possible, but it will make for a full day on the road.
Break Rhythm
2 planned breaks
Plan on a short reset every 3 to 4 hours to stay fresh behind the wheel.
Midpoint
225.6 miles from Spearfish, SD
A natural place for your longest stop of the day
, about 3h 38m into the drive
.
Main Roads
Road
Distance
Duration
I 90
337.5 mi
5h 21m
SD Highway 25
83.8 mi
1h 38m
US Highway 212
14.5 mi
18m
9th Avenue Southwest
6.4 mi
8m
SD Highway 34
6 mi
7m
4th Street
1 mi
1m
South Broadway
0.7 mi
1m
East Jackson Boulevard
0.5 mi
1m
Longest stretch:
I 90
— 337.5 mi, about 5h 21m
Traffic on I-90
Hour-of-day weekday pattern from 86 FHWA count stations on your route.
Peak
4 PM
~640 veh/hr typical
· worst 1,010
Quietest
2 AM
~27 veh/hr
Peak-to-quiet ratio
23.7×
busier at peak than in the quiet hours
12a6anoon6p11p
Averaged across 103 weeks of 2023 FHWA Travel Monitoring Analysis System data. Weekday hours only (Mon–Fri).
Turn-by-Turn Driving Directions
Step-by-step road directions between Spearfish, SD and Watertown, SD.
1
Start on I 90 Business
85 ft·30 sec·North Main Street
2
Continue on I 90 Business
166 ft·9 sec·North Main Street
3
Turn right onto East Jackson Boulevard
0.5 mi·1 min·East Jackson Boulevard
4
Take the ramp
0.3 mi·37 sec
Toward I 90 East, US 85 South
5
Merge onto I 90; US 14; US 85
14 mi·14 min·I 90; US 14; US 85
6
Continue on I 90; US 14; SD 34
7.6 mi·7 min·I 90; US 14; SD 34
7
Continue on I 90; US 14; SD 79
24 mi·24 min·I 90; US 14; SD 79
8
Continue on I 90; US 14; US 16 Truck; SD 79
292 mi·4 hr 35 min·I 90; US 14; US 16 Truck; SD 79
9
Take the exit
0.3 mi·47 sec
Toward SD 25: Emery, Farmer
10
Turn left onto SD 25
24 mi·27 min·SD Highway 25
11
Turn right onto SD 25; SD 34
6.0 mi·7 min·SD Highway 34
12
Turn left onto SD 25
60 mi·1 hr 10 min·SD Highway 25
13
At end of road, turn right onto US 212; SD 25
3.9 mi·5 min·US Highway 212
14
Continue on US 212
1.0 mi·1 min·4th Street
15
Continue on US 212
11 mi·12 min·US Highway 212
16
Continue on US 212
6.4 mi·8 min·9th Avenue Southwest
17
Turn left onto South Broadway
0.7 mi·1 min·South Broadway
18
Arrive at destination
South Broadway
Trip Plan
Given the 7h 40m estimated driving time, starting your day in Spearfish after a good breakfast is recommended to make the most of daylight. You'll have two planned stops, which should be sufficient to break up the 451.1 miles. The longest stretch is 337.5 miles on I 90, so plan your first significant break before or around the end of that segment. Fuel costs are estimated at $69, so ensure your tank is topped off before leaving Spearfish, as fuel availability might be more spread out once you transition to SD Highway 25 and US Highway 212.
Morning Departure
Start early — leave by 6-7 AM to arrive at a reasonable hour.
Evening Departure
This is a long drive — plan for a morning departure or consider splitting it into two days.
You can normally do this drive in one day.
Plan roughly 2 meaningful breaks for fuel, food, and rest.
The halfway point lands around 225.6 miles from Spearfish, SD, or about 3h 38m into the drive.
The longest continuous stretch on this route runs about 337.5 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 99 miles or 1h 38m in
Use this first pause for coffee, a restroom break, and a quick traffic check ahead.
Halfway reset
Around 225.6 miles or 3h 38m in
This is the best place for your longest stop, a real meal, and a full fuel check.
Final approach
Final hour starts around 6h 26m
Traffic, exits, and arrival timing usually matter more near Watertown, SD than in the middle of the route.
Before You Leave
+
Open the route before leaving Spearfish, SD 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.
+
Pick one backup stop option before the midpoint in case traffic changes your pacing.
Day 1
Settle into the route from Spearfish, SD
This is one driving day of about 451.1 miles and 7h 40m.
Your first comfortable stop window is around 99 miles from Spearfish, SD.
This route can stay practical as a one-day drive if traffic stays reasonable.
Plan about 2 real breaks rather than only quick fuel stops.
The longest stretch is on I 90 for about 337.5 miles.
Where to Stop
Rest stops, refuel points, and overnight suggestions along this route.
Place data sourced from public business listings. Hours and availability may vary.
Heads-up: tricky spots
5 of 10
5 decision points cluster between mile 0 and 428.5 — GPS handles the exact turns, but know they're coming. Your lane choice matters more than the turn itself.
4
0 mi into trip|~0m in|East Jackson Boulevard
Turn right onto East Jackson Boulevard
Navigation decision point
5
0.6 mi into trip|~2m in
Take the ramp toward I 90 East, US 85 South
Multiple destination signs - pick the right one
Toward I 90 East, US 85 South
5
338.3 mi into trip|~5h 24m in
Take the exit toward SD 25: Emery, Farmer
Exit ramp - move to the correct lane early. Multiple destination signs - pick the right one
Toward SD 25: Emery, Farmer
4
338.7 mi into trip|~5h 25m in|SD 25 / SD Highway 25
Turn left onto SD 25 / SD Highway 25
Navigation decision point
5
428.5 mi into trip|~7h 10m in|US 212; SD 25 / US Highway 212
At end of road, turn right onto US 212; SD 25 / US Highway 212
Navigation decision point
Fuel & Cost
Regular Gas
$75.25 one way
$150.50 round trip
$4.24/gal25.4 MPG avg158 kg CO2
Fuel Type
$/gal
One Way
Round Trip
midgrade
$4.61
$81.78
$163.57
premium
$5.26
$93.40
$186.80
diesel
$6.18
$109.74
$219.48
No toll roads detected on this route.
Estimated Trip Cost (one way, 1 person)
Fuel
$75
Meals
$25–$50
Total
$100–$125
Rough estimate based on US averages. Hotel $80–$140/night, meals $25–$50/day.
Estimated CO2 emission: 157.8 kg one way.
Prices: EIA weekly data, 2026-10-12.
Station data from NREL Alternative Fuel Stations database.
Driving Electric?
About $47 in charging
· 1 stop
· 66% less CO2
Vehicle Type
kWh
Stops
DC Fast
Home Charge
Average EV
135.3
1
$47.37
$21.65
Efficient EV
112.8
1
$39.47
$18.04
EV Truck/SUV
180.4
2
$63.15
$28.87
Gas CO2
158 kg
EV CO2
53 kg (66% less)
Plan for 1 charging stop. A 30-minute DC fast charge mid-route should be enough to complete the trip comfortably.
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 Oct 18, 2026
Origin
Spearfish, SD
Morning
in Spearfish on Sunday
Local time
7:54 AM
MDT
Current temp
48°F
Mostly Clear
SW 2 to 6 mph0% chanceLive forecast
Destination
Watertown, SD
Morning
in Watertown on Sunday
Local time
8:54 AM
CDT
Current temp
44°F
Partly Cloudy
S 13 mph0% chanceLive forecast
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
1 hour later
The destination clock does not match departure time, so double-check hotel check-in windows and late arrival plans.
Temperature spread
4 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
7h 40m on the road
Start early — leave by 6-7 AM to arrive at a reasonable hour.
Weather data from the National Weather Service. Conditions may change; check closer to your travel date.
National Parks Near This Route
Worth a detour if your schedule allows.
Mount Rushmore National Memorial
National Memorial
Majestic figures of George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln, surrounded by the beauty of the Black Hills of South Dakota, tell the story of the birth, growth, devel...
19 mi from route
~48 min detour
Free
near mile 46.7
The rugged beauty of the Badlands draws visitors from around the world. These striking geologic deposits contain one of the world’s richest fossil beds. Ancient horses and rhinos once roamed here. The...
25 mi from route
~62 min detour
$30
near mile 93.3
Park data from the National Park Service API. Alerts update every 2 hours.
More Details
What kind of drive is this?
You'll spend approximately 98% of your 451.1 miles on highways, primarily on I 90. The longest continuous stretch on a single highway is 337.5 miles along I 90. After this extensive highway cruising, you'll transition to surface roads like SD Highway 25 and US Highway 212. Expect a generally rural feel with fewer exits during the surface road portion compared to the interstate.
98% highway — fuel and pacing are the main things to plan.
18 navigation steps total — most of the decisions cluster near the start and finish.
Longest single stretch: 337.5 mi on I 90.
How Hard Is This Drive?
4/10
This is a straightforward highway drive that stays mostly on I 90 and SD Highway 25. There are only a few real navigation decisions along the way. The trickiest moment comes early in the drive near East Jackson Boulevard.
Driving Effort4/10
Easy - simple navigation with a manageable amount of wheel time
Balances navigation complexity with total wheel time.
The route itself is not hard, but at 7h 40m, endurance matters. Plan breaks every 2-3 hours. The 10 decision points are all manageable with basic attention.
Where does it get tricky?
The main spots that need attention: near the start (East Jackson Boulevard): Navigation decision point; at 0.6 miles: Multiple destination signs - pick the right one; at 338.3 miles: Exit ramp - move to the correct lane early. Multiple destination signs - pick the right one.
Elevation Profile
Gently rolling terrain
3,643 ft1,290 ft
Total Climb
481 ft
Total Descent
2,387 ft
Highest Point
3,643 ft
Elevation Range
2,353 ft
Towns Mentioned on Route Signs
Based on OSRM destination-sign hints, not a full list of every settlement the road passes.
On the drive from Spearfish, SD to Watertown, SD, road signs begin pointing toward Farmer along the way.
Spearfish is in the Black Hills of South Dakota. Although Spearfish is a small community with 14,000 residents, it is the commercial and academic center for several towns in the Black Hills and nearby Wyoming and Montana, attracting more than a million visitors each year with its museums, festivals and natural beauty.
The longest stretch is about 337.5 miles on I 90. The full list of main roads is in the Roads section above.
Yes — we found about 21 rest areas or service plazas within a short detour of the route (from OpenStreetMap). See the Rest Stops tab under Nearby Places for locations and mile markers. Plan to stretch, use the bathroom, and top off fluids every 2–3 hours on longer drives.
It helps. This is a long drive, so arriving tired and in the dark compounds. If the last hour of the trip is on surface roads or mountain grades, aim to arrive at Watertown, SD before sunset when you can. Check the Trip Plan for departure windows that land you in daylight.
Only with planning. This is a long drive for kids — consider splitting it into two days rather than pushing through. Plan at least 2 meaningful breaks. There are 21 rest areas along the route for bathroom stops.
Mostly yes along the main roads, but rural stretches through SD can have sparse or no coverage. Before you leave, download offline Google Maps or Apple Maps for the route, and consider downloading music or podcasts instead of streaming. If you depend on data for navigation, keep a paper backup of the turn-by-turn directions.
The main spots that need attention: near the start (East Jackson Boulevard): Navigation decision point; at 0.6 miles: Multiple destination signs - pick the right one; at 338.3 miles: Exit ramp - move to the correct lane early. Multiple destination signs - pick the right one.
Yes — Mount Rushmore National Memorial and Badlands National Park. See the National Parks section for detour distances and tips on detours.
Not recommended in a single day. At 7.7 hours each way, a round trip means 15.4 hours of driving — that is an unsafe level of fatigue for most drivers. Plan at least one night at Watertown, SD before the return drive.
