Every Day has a variety of settings because the main character spends his life waking up in a different body each morning.
At the beginning of the novel, it is Day 5994. This means that the narrator has woken up in 5994 different bodies in different homes in different areas. The first thing he has to do is figure out who he is, where he is, and how to get through the day. He's in the body of a guy named Justin. They're in Maryland and about an hour from the ocean. It's September.
The day before—Day 5994—the narrator thinks he was in a town about two hours away from the one he wakes up in as Justin.
The narrator explains that he doesn't usually go very far between days. This means that most of the novel takes place on the East Coast of the United States of America. The narrator spends most days that he isn't near Rhiannon trying to find a way to get to her and spend time with her.
At the end of the book, when the narrator decides he has to move on, he wakes up in the body of a girl named Katie. He decides to get as far away from where he is as he can so that he can stop trying to reconnect with Rhiannon. He knows if he stays, he'll be tempted to take over a body for good—which he considers murder.