O'brien Trail Races

O'Brien Trail Races : William O'Brien State Park

O'Brien Trail Races take place at William O'Brien State Park in Marine on Saint Croix, Minnesota on September 26, 2026. The event offers multiple trail distances and uses the park visitor center as the race hub. Parking and bathrooms are located at the Visitor Center. Packet pickup is available race morning only.

The main ultramarathon is a 50K run that uses two 25k loops through the park, including the upper and south sections and Jackson Meadows. Aid stations are provided on the 50K course with four stations per loop. The 50K has an overall finish cutoff of nine hours and requires a specified first-loop cutoff to begin the second loop. Drop bags are accepted at the start/finish area only. Awards are given to top male and female finishers in select distances.

The shorter events use wide grass trails and include one large hill with a flat finish. The 5k and 10k have no aid stations, no awards, and no race shirts, but all finishers receive a full color 8.5 by 11 inch print of the event logo. General post-race food and bottled drinks are provided. External music is not allowed unless headphones are used.

Online registration opens on November 28, 2025 and is available through September 21, 2026; race day registration is also available. Entry fees vary by distance and registration date. There are no refunds, and entries cannot be transferred or deferred. If the event must be canceled for public health or other reasons it may be converted to a virtual event and race items will be mailed within one week of the event completion. Visit the organization's website for the most recent information.