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 higher than 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 when the police were cut due to budget cuts.

Josephine County is one of the 36 counties in the U.S. state of Oregon. As of the 2020 census, the population was 88,090. The county seat is Grants Pass. The county is named after Virginia Josephine Rollins (1834-1912), a settler who was the first white woman to live in the county's boundaries. Josephine County comprises the Grants Pass, OR Metropolitan Statistical Area, which is included in the Medford-Grants Pass, OR Combined Statistical Area.