Blue River, IndianaBlue River is an unincorporated community in Polk Township, Washington County, in the U.S. state of Indiana.HistoryA post office was established at Blue River in 1873, and remained in operation until it was discontinued in 1904. In 1890, the population of Blue River was estimated as around 200 residents. In 1900, the population was 25. By 1920, the population was 112. The population was 34 in 1930.GeographyBlue River is located at.