The early history of Dennis is unknown. In 1836, the Winn family was introduced to the Missionaries of the Church of Jesus Christ of Latter-day Saints. They were soon baptized, but Dennis was not baptized until 1839, after the Winn family had moved to Illinois to live with the Saints.
The Winn family lived in Adams County, Illinois, until the assassination of Church President Joseph Smith in 1844. They moved to Iowa to seek safety and stayed until they had the means to move west to the Rocky Mountains.
After his release from the Mormon Battalion, Dennis stayed in California for a year before making the journey to Utah. Dennis married Margaret Bateman on Jan 2, 1849 in Salt Lake City, Utah. In 1860, the Winn family was called to help settle Cache Valley and made Richmond their home.