John Dickinson was a Quaker and an Episcopalian.
He was identified as a Quaker by A Worthy Company: Brief Lives of the Framers of the United States Constitution by M. E. Bradford; A History of Delaware Through its Governors 1776-1984 by Roger A. Martin; and the Library of Congress. A Worthy Company: Brief Lives of the Framers of the United States Constitution by M. E. Bradford was cited as the source stating he was later an Episcopalian. (Source: Ian Dorion, "Table of the Religious Affiliations of American Founders", 1997).
From: Robert G. Ferris (editor), Signers of the Constitution: Historic Places Commemorating the Signing of the Constitution, published by the United States Department of the Interior, National Park Service: Washington, D.C. (revised edition 1976), pages 158-160:
The only "signer" who did not actually pen his name to the Constitution, because illness caused his early departure from the Convention, he [Dickinson] authorized a fellow delegate [George Read] to do so on his behalf. Nevertheless, he served on the committee on postponed matters and helped arrange the Great Compromise.
Dickinson, "Penman of the Revolution," was born in 1732... In 1753 Dickinson went to England to continue his studies at London's Middle Temple. Four years later, he headed back to Philadelphia and became a prominent lawyer there...
Dickinson lived for two decades more, but held no public offices. Instead, he devoted himself to writing on politics, and in 1801 published two volumes of his collected works. He died at Wilmington in 1808 at the age of 75 and was entombed in the Friends Burial Ground [a Quaker cemetery].
Note that numerous sources and authoritative references have been consulted in order to ascertain the religious affiliation of the American Founding Fathers. Note that the excerpts and references mentioned on this page are not the only references used in order to identify this person's religious affiliation.