State Park / State Forest
Near Big Arm, Montana: $24–$45/night, rigs to 50 ft. Open May through September. Book 9 months ahead via MT State Parks portal.
State Park / State Forest
Managing authority
Near Big Arm, Montana
How much does camping at Big Arm Unit (Flathead Lake SP) cost, and when is it open?
Big Arm Unit (Flathead Lake SP) near Big Arm, Montana (State Park / State Forest) — camping fee $24–$45/night, season May through September, RV size limit Up to 50 ft. Reservations: 9 months ahead via MT State Parks portal — book direct through the official channel.
The numbers
Fee range
$24–$45/night
Season open
May through September
RV size limit
Up to 50 ft
Reservation window
9 months ahead via MT State Parks portal
The insider read
Largest Flathead Lake state-park unit. Wild Horse Island day-trip from the marina — wild horses + bighorn sheep. Sites on the bluff have the dawn lake view.
Original analysis from PickRV — synthesised from public sources you can verify, pulling the operational details competitor guides typically skip.
Verify at fwp.mt.govOn site
Book it right
PickRV doesn't handle campground bookings — reserve direct through the official channel so policies and cancellations flow through one record.
Opens montanastateparks.reserveamerica.com
Every fact above is sourced from the managing agency's canonical page. Cross-check fee, season, and size limit before you depend on them.
Match the campground's size limit and hookup level to a vehicle category, then plan the rest of the trip.
Keep exploring
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BLMInsider tip · Free BLM dispersed sites along the Yellowstone River — sunrise on the Absaroka Range. Pack out everything. Closest free camp to Yellowstone's north entrance.
Near Babb
NPSInsider tip · 'Switzerland of America' — Many Glacier valley with the most grizzly density in the park. Vehicle reservation required for Many Glacier Rd late May - early Sept. Iceberg Lake hike (10 mi) from camp.
Near West Glacier
NPSInsider tip · Largest Glacier NP campground (194 sites). Lake McDonald shore — boat rentals at Apgar village. Going-to-the-Sun Road shuttle stop at the camp entrance.
Near West Yellowstone
NPSInsider tip · Closest reservation-required Yellowstone camp to West Yellowstone entrance. Madison River + meadow has elk + bison routinely. Geyser-basin loop within 14 miles.
Nearby & related
Sourced costs, campground directories, and the places worth a detour — the next layer of Montana trip planning.
Before you go
Montana rules
Verified 2026-05-10