[1] After attending Rock River Seminary, Johnson moved to Prairie du Chien, Wisconsin, in 1848.

He returned to the practice of law in 1856, forming a partnership with W. R. Bullock, a nephew of John C. Breckinridge.

After the legislative session ended, in the fall of 1861, he worked as an assistant to Wisconsin Attorney General James Henry Howe.

[2] In November 1862, he moved to Milwaukee and, for the next 16 years, practiced law with a number of different legal firms in the city.

He served in various local offices over the next decade, as city attorney and member of the Milwaukee School Board.