The group originally consisted of the family of Arthur A. Denny, who left Cherry Grove, Illinois on April 10, 1851. The original party included his father, stepmother, and two older brothers, who eventually stayed on in the Willamette Valley of Oregon, as well as his younger brother David Denny, Arthur Denny's wife (who was also his step-sister, and who was pregnant throughout the journey) Mary Ann Boren, her younger sister Louisa (who would marry David Denny in 1861), and her brother Carson Boren.
Denny is reported to have been quite ill throughout the journey, but remained firmly the group's leader.
On July 6, 1851, they escaped unscathed from a battle with Indians at American Falls on the Snake River. The following day, they met up with John Low, who joined the group. Some time in late July at Burnt River in Eastern Oregon, they encountered a man named Brock, who convinced Denny that Puget Sound would be a good place to found a town.
They arrived in Portland, Oregon on August 22, 1851, with Denny too ill to travel further and Mary Ann nearly ready to give birth. On September 2, she gave birth to a son, Rolland H. Denny.
With the Denny couple laid low, John Low and David Denny headed north to scout the possibilities. Along the way they were joined by Leander "Lee" Terry. In the newly founded settlement of Olympia, Washington, they met Mike Simmons, the already wealthy founder of Tumwater, Washington, who guided them to Alki as a possible site for a settlement. On September 28, 1851, they began building a cabin with help from the local Indians. Terry and Low staked claims; then Low headed back to Portland to get the others, Terry headed out exploring (ostensibly looking for a frow to make cedar shake shingles), and David Denny stayed on in the unfinished cabin. Like his brother, his health wasn't the best, and was doubtless not improved by staying in an unroofed cabin; it was only made worse when he injured his foot with an axe.
In Portland, Denny recruited Illinois farmer William N. Bell and his wife, and, by utter coincidence, Charlie Terry, Leander Terry's older brother. The Terry brothers, from Waterville, New York, had come west as part of the California gold rush, but had not liked the rough and tumble of San Francisco.
On November 5, 1851, the Denny Party left Portland on the schooner Exact. After a difficult passage, particularly hard on the still-ill Denny, they arrived at Alki November 13, where David greeted them with the words, "I wish you hadn't come."
Denny was bitterly disappointed that Low and Lee Terry had already staked the relevant claims for Alki. However, he had no choice but to pitch in, finish the cabin and settle in for the winter. Denny convinced Bell and Boren that they needed to scout a different location. Once the worst of winter cleared, Denny (and sometimes the others) went exploring as far as Commencement Bay (now the site of Tacoma), Port Orchard, Smith Cove, and up the Duwamish River to the present site of Puyallup, before settling on an island in the mudflats near the east shore of Elliott Bay, near the south end of what is now Downtown Seattle.
For the next three years Charlie Terry, who bought out his brother and Low, was the leader of the community at Alki and Denny (along with rival "Doc" Maynard) of what was to become the city of Seattle. However, when it became clear that the tides at Alki were too strong to allow the building of piers, Terry moved to Seattle proper as well.