Lac Castor Numéro Un is a Lake located in Ferland-et-Boilleau; Le Fjord-du-Saguenay, Quebec.

• Latitude: 48° 11' 27'' North   (decimal: 48.1908333)
• Longitude: 70° 45' 26'' West   (decimal: -70.7572222)
• Topography Feature Category: Lake
• Geographical Feature: Lac
• Canadian Province/Territory: Quebec
• Location: Ferland-et-Boilleau; Le Fjord-du-Saguenay
• Atlas of Canada Locator Map: Lac Castor Numéro Un
• GPS Coordinate Locator Map: Lac Castor Numéro Un Lat/Long