hsister adopted 1946/47 Everett, WA

I am searching for my half-sister. She was born in Clatskenie, Oregon 12/26/1942, and was adopted in Everett, Washington in 1946 or 47. My mother was hospitalized for a long period of time, and felt it best at the time to let the family who cared for her adopt her. We would like to find her now, if possible. Her name was Darmalee Jeanne Thompson at birth, and her adoptive parents were Mr & Mrs George Anderson, so her name was probably changed to Anderson. I would also like to know what difference it might make in my search that she was born in Oregon, then adopted in Washington. Would birth records still be in Oregon? That part confuses me, since she was adopted as a child, not an infant. Thanks so much for any help! Sally:thanks: