From the Wikipedia article on Jaywalking:
According to one historian, the earliest known use of the word jaywalker in print was in the Chicago Tribune in 1909. The term’s dissemination was due in part to a deliberate effort by promoters of automobiles, such as local auto clubs and dealers, to redefine streets as places where pedestrians do not belong.
Originally, the legal rule was that “all persons have an equal right in the highway, and that in exercising the right each shall take due care not to injure other users of the way.” In time, however, streets became the province of motorized traffic, both practically and legally. Automobile interests in the USA took up the cause of labeling and scorning jaywalkers in the 1910s and early 1920s; a counter-campaign to name (and disapprove of) “jay drivers” failed.