Mount McKay is a mafic sill located south of Thunder Bay, Ontario, Canada, on the Indian reserve of the Fort William First Nation.

[6] Mount McKay is composed of shale and greywackes – the Rove Formation – which is covered by the hard, protective 60 m (200 ft) thick diabase cap.

[6]: 32 The north face of Mount McKay shows evidence that below this cap is another 7.2 m (24 ft) thick sill of very hard diabase.

[6]: 32 A lookout exists on the lower eastern plateau at an elevation of 300 metres (980 ft), providing a view of Thunder Bay and the city's harbour.

A small, unmaintained trail can be used to reach the top from the lookout via the north face, with a heavy gauge steel cable that can be used for support.