As the regulation of carbon dioxide emissions play an increasingly important role in fighting against global warming, tracking carbon dioxide emissions trends, estimating the determinants of driving emissions, and identifying opportunities for reducing emissions will be necessary. This paper studies the relationship among carbon dioxide emissions, energy consumption and economic growth in United States at state level during the period from 1960 to 2011. It is essential to study state level determinants of carbon dioxide emissions especially for a country that differs from coast to coast in energy use, economic development strategy, and carbon dioxide reduction policy. Based on the EKC long run analysis of CO2 emissions in each state of US, we found that 13 states show inverted-U relationship between CO2 emissions and economic development, 18 states display N relationship, 6 states indicate increasing linear relationship, 6 states appear decreasing linear relationship, and the rest states show no cointegration among the variables. We also found that energy consumption always having significant and positive effect on carbon dioxide emissions. States in US have already tried a variety of strategies to reduce emission over the past decades, vary by state results of estimated EKC relationship may help indicate the past successes and failures of efforts, and provide guidance for future environmental policy.