Prior to 1998, Highway 118's western terminus was former provincial Highway 169 at Glen Orchard, making the total road length 116.1 km from that point to Haliburton. Today, the road between this point and provincial Highway 11 is Muskoka Region Road 118.
Before 2003, Highway 118's eastern terminus was at Haliburton, junction of the former provincial Highway 121. In 2003, the existing provincial Highway 121 east of Haliburton was renumbered to extend Highway 118's eastern terminus. This portion of the highway follows the historic Monck Road colonization road.
Highway communities between the current western and eastern ends are Uffington (a short distance off Highway 118), Vankoughnet (also nearby, off-route), Carnarvon, West Guilford, Haliburton, Tory Hill, Cardiff