Jacob’s younger brother David became a close associate of Joseph Smith, Jr.. In June 1829, Jacob Whitmer joined his brothers as one of the Eight Witnesses. He was baptized into the church on April 11, 1830.
He gathered with early church members to Jackson County, Missouri, but was driven by non-Mormon vigilantes from his home there and later from his home in Clay County, Missouri as well. He then settled in Caldwell County, Missouri where he served on Far West’s High Council. He was excommunicated from The Church of Jesus Christ of Latter-day Saints in 1838 along with the entire Whitmer Family.
He settled finally near Richmond, Missouri in neighboring Ray County, Missouri where he worked as a shoemaker and a farmer. He died on April 21, 1856 still affirming his testimony of the Book of Mormon.
Source: www.MormonWiki.com (used by permission)