(1878)
"A Supreme Court of the United States case that held that religious duty was not a suitable defense to a criminal indictment. George Reynolds was a member of The Church of Jesus Christ of Latter-day Saints, charged with bigamy after marrying Amelia Jane Schofield while still married to Mary Ann Tuddenham in Utah Territory" (here).
This is the first US Supreme Court case where the "wall of separation between church and state" phrase is used.