In addition to his legal and business activities, Johnson became involved in local government and politics as a Republican. From 1866 to 1879, Johnson was clerk of the Sacramento County Board of Swamp Land Commissioners, the body charged with planning and overseeing development and reclamation of marshes and bogs throughout the county. In 1867 he was the National Union Party candidate for county auditor; accused of illegal campaign practices for allegedly adding the names of non-existent voters to the rolls so he could cast ballots for himself, Johnson pleaded no contest and withdrew from the campaign. From 1868 to 1871 he was a clerk in the office of the state Surveyor General.
