District boundaries have changed over time. Therefore, senators before 2013 may not represent the same constituency as today. From 1993 until 2003, it covered a slightly different area in eastern Oregon; from 2003 until 2013, it extended to cover Gilliam, Jefferson, Sherman, Wasco, and Wheeler counties and parts of Deschutes and Lake counties; and from 2013 until 2023, it lost all of these gains except western Wasco County, northern Deschutes County, and Jefferson County.
The current district is more compact and adds all of Crook and Lake counties, which have historically been a part of other districts, while losing parts of northern Jefferson County and northern Deschutes County as well as all of Wasco and Wheeler counties.
^Off-cycle election due to the resignation of Ted Ferrioli in 2017 after his appointment by Governor Kate Brown to the Northwest Power and Conservation Council. Cliff Bentz was the incumbent in this election as he was appointed to fill the vacant seat.
^Off-cycle election due to the resignation of Cliff Bentz in 2020 after his election to the House of Representatives representing Oregon's 2nd district. Lynn Findley was the incumbent in this election as he was appointed to fill the vacant seat.