If you're not registered to vote by midnight on Monday, Oct. 6, you're not gonna be able to cast a ballot in this year's election. It's easy as can be online—as long as the state knows you're a citizen—by following this link.
Otherwise, you can find a list of Pima County locations to fill out the form in real life here. And the Pima County Recorder's Office will be doing drive-by voter registration both downtown and in eastside Tucson on Monday, Oct. 6. Read all about the details here and find some unregistered friends to sign up. Your vote, your voice.