A reliable list of state populations can be found on the United States Census Bureau website. It provides estimates for all 50 states and the District of Columbia, current as of July 1, 2014.
California, with approximately 39 million people, is the most populous state. Florida and New York are a distant second and third, with populations in the vicinity of 20 million. There is a tremendous gap between the most and least populated states. Wyoming, Vermont, South Dakota, North Dakota, Delaware, Alaska, and the District of Columbia all have populations of under 1 million. The United States Census Bureau also offers a breakdown of each population into social, economic, housing and demographic characteristics.