The origin of the park is owed to the conservation efforts of artists.
Canadian Group of Seven  artist A. Y. Jackson was so alarmed by the prospect that Trout Lake (now O.S.A. Lake) was about to be logged that he petitioned the Provincial government of the day to have it preserved.
His letter was received by William Finlayson, then the Minister of Lands and Forests, resulting in a successful conclusion.
 The lake was taken into trust by the Ontario Society of Artists and its name was changed to O.S.A. Lake.
 Jackson's efforts were rewarded with the naming of a lake after him on his 90th birthday.
The hills and lakes in the Killarney area became a popular place for painting and sketching and over the years several other members of the Group of Seven  worked there including Franklin Carmichael, Arthur Lismer and A. J. Casson.
In 1959 the Killarney Park area was set aside as a wilderness preserve.
In 1962 Highway 637 opened, connecting the north shore of Georgian Bay all the way from the town of Killarney to the Trans-Canada Highway.
Finally in 1964, with the help of lobbying efforts by the Group of Seven, 4,000 square miles (10,000 km²) of Georgian Bay shoreline were set aside as a wilderness reserve, and Killarney became a provincial park.

The park has experienced some challenges that threaten the health of its delicate local ecosystems.
Owing in large part to its proximity to Sudbury with its nickel mines and smelters, local lakes were damaged by acid rain.
Pollution caused by the smelting activities associated with nickel mining between the 1940s and the 1970s, caused many of Killarney's lakes to become acidified, resulting in the loss of fish species, algae and aquatic plant life in many of the lakes.
This damage was especially severe in the quartzite areas.
Legislation passed in the 1970s forced the industry to improve its emissions standards.
Since then, sulphur emissions have been reduced by over 90 percent.
To date, water quality has improved in some lakes to pre-pollution levels, while in other lakes the slow process of biological recovery continues.
More recently, the lakes have been under threat from non-indigenous invasive species such as the Bythotrephes longimanus (a.k.a.
spiny water flea), which threaten local species.

In 2006, the provincial government also created the adjacent but separate provincial park of Killarney Lakelands and Headwaters.
In 2015, the Wiikwemkoong First Nation on Manitoulin Island also established the adjacent Point Grondine Park on their own unoccupied heritage territory in the area.
The origin of the park is owed to the conservation efforts of artists. Canadian Group of Seven  artist A. Y. Jackson was so alarmed by the prospect that Trout Lake (now O.S.A. Lake) was about to be logged that he petitioned the Provincial government of the day to have it preserved. His letter was received by William Finlayson, then the Minister of Lands and Forests, resulting in a successful conclusion.  The lake was taken into trust by the Ontario Society of Artists and its name was changed to O.S.A. Lake.  Jackson's efforts were rewarded with the naming of a lake after him on his 90th birthday. The hills and lakes in the Killarney area became a popular place for painting and sketching and over the years several other members of the Group of Seven  worked there including Franklin Carmichael, Arthur Lismer and A. J. Casson. In 1959 the Killarney Park area was set aside as a wilderness preserve. In 1962 Highway 637 opened, connecting the north shore of Georgian Bay all the way from the town of Killarney to the Trans-Canada Highway. Finally in 1964, with the help of lobbying efforts by the Group of Seven, 4,000 square miles (10,000 km²) of Georgian Bay shoreline were set aside as a wilderness reserve, and Killarney became a provincial park.
The park has experienced some challenges that threaten the health of its delicate local ecosystems. Owing in large part to its proximity to Sudbury with its nickel mines and smelters, local lakes were damaged by acid rain. Pollution caused by the smelting activities associated with nickel mining between the 1940s and the 1970s, caused many of Killarney's lakes to become acidified, resulting in the loss of fish species, algae and aquatic plant life in many of the lakes. This damage was especially severe in the quartzite areas. Legislation passed in the 1970s forced the industry to improve its emissions standards. Since then, sulphur emissions have been reduced by over 90 percent. To date, water quality has improved in some lakes to pre-pollution levels, while in other lakes the slow process of biological recovery continues. More recently, the lakes have been under threat from non-indigenous invasive species such as the Bythotrephes longimanus (a.k.a. spiny water flea), which threaten local species.
In 2006, the provincial government also created the adjacent but separate provincial park of Killarney Lakelands and Headwaters. In 2015, the Wiikwemkoong First Nation on Manitoulin Island also established the adjacent Point Grondine Park on their own unoccupied heritage territory in the area.
Killarney Provincial Park