How long until you become a legal resident of Oregon?

[lintun]

I moved to Oregon from Washington on February 1st, 2012 and changed my address during that first week. I'm trying to go back to school, so I'm applying for financial aid and they need to know when I became a legal resident of Oregon. I receive mail to my new address, but that's the only thing that has changed. I don't have Oregon license plates (the car is under my father's name in Washington). Also, I still have my Washington drivers license. Help!