James Street, one of the first streets platted in Seattle on May 23, 1853, was named by Arthur Armstrong Denny after his younger brother, James Marion Denny (1824–1854). Histories of Seattle report that James was too sick to leave Oregon and come to Puget Sound with the Denny Party and, indeed, he died in the town of Sublimity, Oregon, just a year after the street was named for him. Nothing I have found reports an actual cause of death. Marion Street is also named after this brother.
James Street runs ¾ of a mile from Yesler Way just east of 1st Avenue to an alley just east of Broadway. It appears east of there in a few short stretches and finally as a stairway from 38th Avenue to Lake Washington Boulevard at Madrona Park.