The communities of Bridgeport, Brewster and Pateros in North Central Washington decided in 1947 and 1948 that a 12 bed hospital was needed. All three communities solicited funds and hosted fundraising projects. After the project began financial difficulties developed and the Board of Directors realized that the formation of a hospital district was the only answer to their dilemma. The District was formed and tax monies made it possible to complete the 12 bed facility, which opened January 12, 1949. 
On March 2, 1951 the facility was dedicated as McKinley Memorial Hospital, in honor of Dr. Charles R. McKinley, one of the first physicians in the area.
In 1954, a waiting room and offices were added to the hospital and 26 patients were being treated in the 12 bed facility. 
With the construction of Chief Joseph Dam in Bridgeport and an influx of new residents in all three towns, it soon became apparent the hospital was no longer adequate and could not be made so by state standards, so plans began for a new hospital.
The hospital district boundaries at the time included Duley Lake, Monse, Brewster, Pateros and the lower Methow areas; however, patients were coming from northern Douglas County as well as the upper Methow Valley. It was decided that the first step toward expansion was to enlarge the District. This was done by consolidating District # 2 (upper Methow to Mazama) and annexing the Douglas County areas around Bridgeport and Mansfield. A name for the new district area was needed, so hospital Administrator, Howard Gamble, 
named the district: Okanogan Douglas County District Hospital
The new 35 bed hospital was opened on June 13th, 1959 after a bond issue was authorized by the voters. As an additional part of that bond, the voters also agreed to a remodel of the old building into a 36 bed nursing home that was completed at a later date. 
With the opening of a new private assisted living facility in Brewster in 1969, all of the nursing home residents were moved, allowing for the utilization of the old hospital for ancillary departments including Physical Therapy and Medical Records, plus a Conference Room and offices for Purchasing and Administration.
In 1973, again due to an extreme bed shortage and the need to enlarge and remodel some areas to meet improved building and operation standards, the voters again authorized expansion of the facility to 50 beds, which was accomplished with extensive remodeling in the 1959 construction. This construction allowed the hospital to have new surgery suites, a surgical recovery room, a completely separate coronary care unit, a pediatrics room, an enlarged laboratory space, and larger waiting room. 
The voters authorized the construction of an 8 bed Intensive Care Unit in 1984. This addition, plus some remodeling, left the hospital with a total of 48 beds.
In 1986 the West Wing was converted from patient rooms to ancillary service areas, and in 1987 a Nuclear Medicine department was added. In 1988, Radiology and Respiratory Therapy were moved and remodeled, leaving a 43 bed facility. From 1998 through 2010, Okanogan Douglas District Hospital 
continued adding services requested by hospital district residents to help support their health and lifestyles by opening the HealthBeat Fitness Center, Advantage Durable Medical Equipment, and the Health and Wellness Center. During 2011, the business and Administration offices were moved into the Hillcrest building at the North end of the campus to provide easier access and help allow space for needed renovations elsewhere in the hospital.
Towards the end of 2011, the Board of Commissioners decided it was time to change the name of the hospital. A public contest was held within the district and from more than 100 contest entries, the name “Three Rivers Hospital” was selected. While the official name of the hospital remains “Okanogan Douglas County District Hospital” we are moving forward and doing business as 