Wind power in Illinois provided 4.7% of the state's electrical power in 2013. At the end of 2012, Illinois had 3568 megawatts (MW) of wind power installed, ranking fourth among states for installed wind turbine capacity.
Wind power has been supported by a renewable portfolio standard, passed in 2007, and strengthened in 2009, which requires 10% renewable energy from electric companies by 2010 and 25% by 2025. Illinois has the potential for installing up to an estimated 249,882 MW of wind generation capacity at a hub height of 80 meters. A 2005 wind map shows that most of the state has class 2 and class 3 winds, and that utilizing the 1.2% of the state with the best winds could supply 9,000 megawatts of wind power.
The first wind farm in Illinois opened in 2003 and by 2009, it had over 1800 MW installed statewide with thousands of MW more in the planning stages. The largest wind farm in the state is the 300 MW Cayuga Ridge installation, while another seven windfarms each exceeded 100 MW capacity. The Twin Groves Wind Farm was the largest wind farm east of the Mississippi when completed but has since been surpassed. Some smaller installations include a 0.66 MW turbine at the Bureau Valley School District and a 2.5 MW turbine at the Illinois Sustainable Technology Center, formerly part of the Illinois Department of Natural Resources, now part of the University of Illinois. A proposed high voltage DC transmission line would transmit wind generated electrical power to the Chicago area from northwest Iowa.