California leads the list as the most populous state in the U.S., with an estimated population of over 39 million in 2025. While growth has slowed down in recent years, even to the point of a slight decline, California is still significantly larger than Texas and Florida, the next two largest states. The sheer number of people in California is due to a combination of factors, including a strong economy, its world-class cities such as Los Angeles and San Francisco, and a strong flow of international migrants, which account for 12% of the country’s total population.