Deism

Deism is a view that the course of nature sufficiently demonstrates the existence of God. For deists formal religion is superfluous, and deist scorn as spurious claims of supernatural revelation. Their tenets stemmed from the rationalism of the period of the Enlightenment, and though the term is not now generally used, the tenor of their belief persists. 

The term freethinkers is almost synonymous. Voltaire and J. J. Rousseau were deists, as were Benjamin Franklin, Thomas Jefferson, and George Washington.

See E. R. Pike, Slayers of Superstition (1931, repr. 1970); G. A. Koch, Religion of the American Enlightenment (1933, repr. 1968).