Lac-Nilgaut is a large unorganized territory in the Outaouais region, Quebec, Canada.

With a surface area of 9,851 km2 (3,803 sq mi), it makes up over 70% of the northern portion of Pontiac Regional County Municipality.

The eponymous Lake Nilgaut is located roughly in the centre of the territory, at an altitude of over 300 metres (980 ft).

This 9 kilometres (5.6 mi) long lake is named after the nilgai (French: nilgaut), the largest Asian antelope and only found on the Indian subcontinent.

The name was officially introduced in 1935, but it is unknown why this term was chosen to replace the original name Lac à l'Orignal (Moose Lake).