History of Secondary Highway 525 (#1):
The first Secondary Highway 525 was a local highway in the District of Muskoka that provided access from Gravenhurst to the Muskoka Sanitorium, located a short distance north of town. Highway 525 was first depicted on a Preliminary Route Plan prepared by the Department of Highways of Ontario (DHO) in May, 1956. The route, which had been known previously as Sanitorium Road, was designated by an Order-in-Council dated May 9, 1956. Highway 525 was 1.5 miles (2.4 km) in length. The highway was already paved at the time of designation in 1956. The entire route of Highway 525 was under the jurisdiction of the DHO, except for a small section of the highway lying within the Town of Gravenhurst. The short section of Highway 525 from Highway 11B (Winewood Avenue) to the former town limits at Old Muskoka Road was under municipal jurisdiction. This non-assumed section of the highway was designated as a Municipal Connecting Link by an Order-in-Council, effective October 9, 1958. The route of Highway 525 remained unchanged for many years.
Up until 1971, there was no intermediate road agency between the DHO and the local townships within Muskoka District. The creation of the District Municipality of Muskoka on January 1, 1971, changed the way road services were administered within the District. As a result, many of Ontario's Secondary Highways lying within the District were transferred to this newly-formed tier of municipal government, particularly those which served as local access highways. Highway 525 served only a local purpose, as it was a dead-end highway at the Ontario Hospital. The route of Highway 525 was transferred to the new District Municipality of Muskoka, effective April 30, 1972. The former Municipal Connecting Link section of Highway 525 through Gravenhurst was formally revoked by an Order-in-Council, effective February 2, 1972. Although the first route of Highway 525 ceased to exist in 1972, another unrelated Highway 525 was established in Northwestern Ontario north of Kenora in 1981.