James Smith was a Presbyterian.
He was identified as a Presbyterian by the Presbyterian Historical Society and the Presbyterian Church, USA. (Source: Ian Dorion, "Table of the Religious Affiliations of American Founders", 1997).
From: B. J. Lossing, Signers of the Declaration of Independence, George F. Cooledge & Brother: New York (1848) [reprinted in Lives of the Signers of the Declaration of Independence, WallBuilder Press: Aledo, Texas (1995)], pages 119-122:
James Smith was born in Ireland, and was quite a small child when brought by his father to this country... is father, who had a numerous family of children, settled upon the Susquehanna river, in Pennsylvania, and died there in 1761. James was his second son, and, discovering a strong intellect at an early age, his father determined to give him a liberal education. For this purpose, he placed him under the charge of Reverend Doctor Allison, provost of the college of Philadelphia. He there acquired a knowledge of Latin and Greek, and what proved more useful to him, practical surveying...From: Robert G. Ferris (editor), Signers of the Declaration: Historic Places Commemorating the Signing of the Declaration of Independence, published by the United States Department of the Interior, National Park Service: Washington, D.C. (revised edition 1975), pages 132-133:
Mr. Smith was quite an eccentric man, and possessed a vein of humor, coupled with sharp wit, which made him a great favorite in the social circle in which he moved. He was always lively in his conversations and manners, except when religious subjects were the topics, when he was very grave and never suffered any in his presence to sneer at or speak with levity of Christianity. Although not a professor of religion, he was a possessor many of its sublimer virtues, and practised its holiest precepts.
Smith, the second son in a large family, was born in Northern Ireland about 1719. When he was around 10 years old, his father emigrated to America and settled on acreage west of the Susquehanna River in York County, Pa. James studied surveying and classical languages at Rev. Francis Alison's academy in New London, Pa., and then read law in the office of his elder brother at Lancaster...
Smith died at about th eage of 87 in 1806 at York, survived by two of his five chldren. His grave is in the First Presbyterian Church Cemetery.