No longer assigned. State Route 91 was commissioned on Jan. 1, 1932. Its original route, starting at the south end:

• north along today's Route 198, from US 6 in Chaplin to Route 171 in Woodstock
• east along today's Route 171 to US 44 in Putnam

Unfortunately for state Route 91, a new Interstate 91 was designated in 1957. State route 91 was decommissioned in 1959, and its mileage was assigned to Routes 171 and 198.