This API provides state-level population, in addition to the U.S. total population. EIA's State Energy Data System (SEDS) is a comprehensive data set that consists of annual time series estimates of state-level energy use by major economic sectors, energy production and State-level energy price and expenditure data. The system provides data back from 1960. Data are presented in physical units, Btu, and dollars. Users of the EIA API are required to obtain an API Key via this registration form: http://www.eia.gov/beta/api/register.cfm