With one hand on the Bible and the other held high Tuesday afternoon, John T. Wilcher repeated the last four words of his oath of office: “So help me God.” And with that, Chatham County has a new sheriff, and the Johnny Mercer Theatre erupted with applause as roughly 500 people rose to their feet. Wilcher, 71, was the victor of a special election and a runoff to replace Al St Lawrence, the six-term sheriff who died in office last year.