Born on February 14, 1847, in Keokuk County, Iowa, J.J. was the seventh of twelve children born to William Webb, Jr. and Innocent Blue Brown Webb.
In 1862, the family moved to Nebraska and then, later, to Osage City, Kansas. Webb traveled west in 1871, becoming a buffalo hunter and then a surveyor in Colorado. He then drifted from Deadwood, South Dakota, to Cheyenne, Wyoming, to Dodge City, Kansas.