[2] On November 8, 1994, Koster won the election and became a Republican member of Washington House of Representatives for District 39, Position 2.

On November 5, 1996, as an incumbent, Koster won the election and continued serving District 39, Position 2.

On November 3, 1998, as an incumbent, Koster won the election and continued serving District 39, Position 2.

[9] On November 8, 2016, Koster won the election and became a Republican member of the Washington House of Representatives for District 39, Position 2.

[10][6] In July 2017, Koster announced his retirement from the State House to lead the County Road Administration Board as its executive director.