Honest Cattle · Petroleum County
Water Rights
Water Rights & Land Ownership
Petroleum is the least-populated county in Montana — Winnett is the county seat and roughly the entire town. The Musselshell River forms the southern border with Garfield; Box Elder and Flatwillow Creeks drain north toward the Missouri Breaks. Most of the 3,900+ active rights are stock and small irrigation off creeks and ranch wells; the Petrolia Reservoir on Flatwillow Creek serves the largest irrigation footprint.
Combine the DNRC WRQS water-rights record with the Montana Cadastral using the 17-digit geocode that links them.
Active rights pulled live from DNRC WRQS on 2026-06-01. Petroleum spans four DNRC basins: 40A (upper Musselshell tributaries), 40B (Musselshell mid), 40C (Musselshell main), 40EJ (Musselshell-Missouri transition).
Petroleum County Watershed Map
The Musselshell River cuts E-W across the south county. Flatwillow Creek drains the southern Snowy spurs through Petrolia Reservoir north toward the Missouri. Box Elder and McDonald creeks drain the central county toward the breaks.
Search Petroleum County water rights
- Water right format:
- 40A 12345 00 (upper trib.) · 40C (Musselshell main) · 40B/40EJ (mid/lower).
- Primary basins:
- 40A upper Musselshell trib · 40B Musselshell mid · 40C Musselshell main · 40EJ Musselshell-Missouri transition.
- Petrolia Reservoir:
- Backs water for irrigation deliveries downstream on Flatwillow Cr. Active rights for the project sit ahead of new junior diversions on the creek.
- DNRC regional office:
- Lewistown Regional Office, 406-538-7459.
- Clerk & Recorder:
- Petroleum County, 406-429-5311.
Quick links
Data sources: Montana DNRC, MSL/DOR Cadastral, MBMG GWIC. Active rights pulled live from DNRC WRQS on 2026-06-01. Informational only.