What state can I register to vote in?

I m 18 years old (will be 19 in March and by the time or the 2016 presidential election) and am currently not registered to vote. I definitely want to vote in the upcoming election, so I d like to register in time to do so. There s just one problem: I don t know what state to register in.

I have a Philadelphia birth certificate, though I realize that doesn t mean anything here.

I grew up (and reached legal voting age) in Illinois, and currently have a valid Illinois driver s license.

In July, my family moved to Portland, Oregon. My name was included on the lease, so my legal permanent residence has been in the state of Oregon for about six months.

As of September, I m in college at a state school in Massachusetts, where I spend most of the year. My dorm is, obviously, listed as my mailing address.

So what state do I register to vote in? I spend most of the year in Massachusetts, but my legal residence is in Oregon, and my state ID is from Illinois. I assume I need to get an Oregon ID next time I go home, and register in that state, my state of residence, but I wanted to be sure, especially since I m not likely to BE in Oregon at the time of the election.