John and his wife Mary arrived in New Orleans via the ship Buena Vista on 19 April 1849. His niece, Mary Ann Williams, was on the ship with them as well, but did not cross the plains with them. John and his wife were still in Iowa at the time of the 1850 census, enumerated 18 September 1850, and the first documentation to place then in Utah is the 1856 Utah census so they would have traveled some time between 1852 and 1856. Further research is needed to narrow the year of their year of travel and identify the name of the company with which she traveled.
Based on the available sources, it appears that this John and his wife, Mary, along with John's niece, Mary Ann, were all from Europe (probably England, but possibly Wales).
John is the brother of Daniel Edward Williams.