Constantia is a former settlement in Lassen County, California. It was located near the south end of Long Valley 45 miles (72 km) southeast of Susanville.
The Constantia post office opened in 1912 (having been moved from Long Valley and closed in 1927.
- ^ a b c Durham, David L. (1998). California's Geographic Names: A Gazetteer of Historic and Modern Names of the State. Clovis, Calif.: Word Dancer Press. p. 366. ISBN 1-884995-14-4.
Coordinates: 39°57′00″N 120°02′17″W / 39.95000°N 120.03806°W