MacMillan Provincial Park, Provincial park in Vancouver Island, Canada

MacMillan Provincial Park is a 301-hectare provincial park on the western shore of Cameron Lake, central Vancouver Island. It protects the 157-hectare stand of ancient Douglas fir known as Cathedral Grove, where trees reach 9 metres in circumference and some are over 800 years old. The park straddles Highway 4 and the Island Rail Corridor, and its trails pass moss-covered trunks and ferns.

Cathedral Grove was a tourist stop by the 1920s, when the name appeared in correspondence attributed to Governor General Viscount Willingdon. In 1944 H.R. MacMillan donated 136 hectares of his company's timber holdings, and the area became a Class A provincial park in 1947. The park grew from 157 hectares to 301 hectares after 2007.

The name Cathedral Grove was used by Governor General Viscount Willingdon in 1928 and appeared in provincial correspondence that decade. Indigenous peoples used the area for ceremonies before European settlers arrived; bark-stripped western redcedar trees, dated as far back as AD 1137, record that use.

The park is located about 25 kilometers west of Qualicum Beach along the main highway and is easily reached by car. The trails through the forest are well-maintained and accessible for people of different fitness levels.

The forest sits at the boundary between two climate zones, where dry conditions on the east meet wet conditions on the west. This transition point makes the location ecologically distinct and shapes how the trees grow differently on each side.