Tesla Motors is an American company. The Model S is designed and assembled in the United States. Fremont, California to be exact. The factory was originally called New United Motor Manufacturing, Inc. (NUMMI). A joint venture between General Motors and Toyota that did not succeed. Tesla Motors was able to secure this massive plant at a significantly reduced price. One of the things that helped make the Model S a reality.
National Geographic has made a series of megafactories documentaries and covered the Tesla story.
Supplier Business posted this PDF of the suppliers to Tesla in order to build the Model S. I’m sure it was a point in time and this will evolve.
Tesla Motors is a Silicon Valley software firm that makes hardware and it happens to be a car. Sorry. It’s not made in Detroit.