The Lovatt family emigrated to the United States in 1855. The sailed on the ship Emerald Isle. William's obituary indicates that he arrived in Utah in 1860 (see Deseret News 19 May 1875). The first documentation to place them in Utah is the birth of a child in October 1862. Further research is needed to narrow the year of their travel.
Birth date is confirmed by Find A Grave website.