Theaters across the US are willing to let people in dressed up as their favorite villain/princess/Wookie but only up to a certain point.
AMC Theaters: [AMC does not permit weapons or items that would make other guests feel uncomfortable or detract from the movie-going experience. Guests are welcome to come dressed in costume, but we do not permit masks. In short, bring your lightsaber, turn it off during the movie, and leave the blaster and Darth Vader mask at home.]
Regal Cinemas: [Cosplay is welcome- just no mask wearing or weapon-like props in theatres though.]
Cinemark: [Star Wars costumes are welcome. However, no face coverings, face paint or simulated weapons (including lightsabers/blasters) will be allowed in the building.]