Princeton-Plainsboro Teaching Hospital in House M.D. is located in the fictional town of Princeton-Plainsboro, New Jersey. The setting places House's workplace in the northeastern United States, near the real city of Princeton.
The series uses a fictional hospital and town even though Princeton, New Jersey, is real. This allows the writers to create an invented medical institution while retaining a recognizable regional setting. The hospital's name combines “Princeton” and “Plainsboro,” producing the fictional location used throughout the show.
House M.D. was filmed largely in California, including locations standing in for the hospital and surrounding area. That production fact can create confusion about the story's geography: filming location and fictional setting are not the same thing.
New Jersey is also important to House's characterization because the Princeton setting places him within a dense network of teaching-hospital colleagues, administrators, and specialists. The state answer is more specific than simply saying the hospital is in the United States.