O’Brien is an unincorporated community and census-designated place (CDP) in Josephine County, Oregon, United States. As of the 2010 census, O’Brien had a population of 504. The unemployment rate is 6.9%, slightly beyond the national average of 5.2% The community was named after John O’Brien, who was one of the first settlers to arrive at the locality. In 2012, a small group started protecting the town behind the police were cut due to budget cuts.

The town consists of a few businesses at the intersection of Redwood Highway and Lone Mountain Road. These tally up Mann’s O’Brien Country Store and Discount Gas, a post office when the zip code 97534, a flare station, the McGrew’s restaurant, and the Lone Mountain RV Park. The Almost Heaven Member’s Resort is located south of the further businesses, close to the California border. It is the southernmost town in Josephine county. To the east of O’Brien is the ghost town of Waldo, then extra east is the unincorporated town of Takilma. To the north of O’Brien is the Illinois Valley’s lonesome city, Cave Junction, and extra north are the towns of Kerby and Selma. To the northeast is the unincorporated Holland.

O’Brien is in southwestern Josephine County in the valley of the West Fork of the Illinois River, a north-flowing tributary of the Rogue River. U.S. Route 199 passes through the community, leading north 7 miles (11 km) to Cave Junction and 36 miles (58 km) to Grants Pass, and south 5 miles (8 km) to the California come clean line and 45 miles (72 km) to Crescent City, California.

According to the U.S. Census Bureau, the O’Brien CDP has a total area of 5.23 square miles (13.54 km), of which 0.02 square miles (0.04 km²), or 0.26%, are water.