Corporations are both everywhere and nowhere. They are everywhere, first and foremost, on the economic scene: a large percentage of economic activity in the United States is effectuated through the corporate form. But the reach of corporations is far broader than that. Many of our other institutions, including universities, churches, hospitals, and other non-profit organizations, are in corporate form. Other salient features of our society, such as representative democracy, originated from the use of the corporate form in medieval England. Even the idea of the state itself originated in Roman and Medieval legal notions about corporate bodies.
Avi-Yonah, Reuven S. "Corporations, Society, and the State: A Defense of the Corporate Tax." Va. L. Rev. 90, no. 5 (2004): 1193-255.