Born in Pennsylvania, Whitmer moved with his parents to New York, where he married Elizabeth Schott on September 29, 1825. Whitmer and Elizabeth had nine children together, only three of whom survived to adulthood.
Whitmer’s younger brother David became a close associate of Joseph Smith. In June 1829, Jacob Whitmer joined his brothers in signing a statement testifying that he personally saw and handled the golden plates said to be in Smith's possession. On April 11, 1830, he was baptized into the newly organized Church of Christ.
Whitmer settled finally near Richmond in neighboring Ray County, where he worked as a shoemaker and a farmer. He died on April 21, 1856, still affirming his testimony of the golden plates.
Jenson, Andrew (1901). Latter-day Saint Biographical Encyclopedia: A compilation of biographical sketches of prominent men and women in the Church of Jesus Christ of Latter-day Saints. Vol. 1. Salt Lake City, Utah: The Andrew Jenson History Company (Printed by The Deseret News Press). pp. 276–277.