In 1832 after the Blackhawk War he came to the mining district of Dubuque in what was then Michigan Territory, the first year settlers were allowed to cross the Mississippi River into what now is Iowa.
Gillilan became a merchant in the dry goods business,[2] also selling groceries and hardware.
[3] On July 2, 1836, he married Mary Krisier or Kreiser (sources vary); in the marriage announcement it is mentioned that he was the former sheriff of Dubuque County.
The Gillilans moved to the mining district of Potosi in Wisconsin Territory in 1841, and Davis became a miner.
In December 1846 he was a leader of a group of mineral rights claimants who met in British Hollow and organized a vigilance committee to assert squatters' rights over lands in the region which were to be sold by the United States General Land Office in May 1847 "without respect to claims or to settlers, leaving it for speculators to bid off our claims and property which have cost us the labor of years.