CALDWELL, a city of Idaho, U.S.A., in the fertile Boise valley, near the western boundary of the State; the county seat of Canyon county. It is on Federal highway 3o and the Oregon Short Line of the Union Pacific railway system. The population in 1930 was 4,974. It is the centre of a government irrigation project of 144,2ooac., 8o% of which is already under crops. The College of Idaho was established here in 189o.