Illinois has more nuclear reactors than any other state because one utility, Commonwealth Edison, made an aggressive early bet on nuclear power in the 1960s and kept building. That decision was driven by economics, geography, and timing. Today, 11 commercial reactors operate across six sites in the state, producing nearly 54% of Illinois’ electricity and more nuclear megawatts than any other state in the country.
Commonwealth Edison’s Early Gamble
The story starts with Commonwealth Edison, the Chicago-area electric utility that would eventually become part of Exelon (now Constellation). In 1960, the company brought Dresden 1 online, a 200,000-kilowatt reactor southwest of Chicago. It was among the earliest commercial nuclear plants in the nation, and it gave ComEd something no competitor had: a head start.
That head start compounded. By getting in early, ComEd locked in nuclear fuel contracts and reactor purchases at prices that looked increasingly cheap as costs rose industry-wide. In its 1968 annual report, the company noted it had purchased four of its six planned nuclear units on firm-price, turnkey contracts averaging just $118 per kilowatt. By 1974, the company estimated its nuclear fleet would save $10 million a year in capital and operating costs compared to coal plants of the same era. ComEd’s leadership described themselves as “the nation’s leading nuclear power company,” and that wasn’t bluster. Their early commitment let them recruit top nuclear engineers and scientists, building institutional expertise that made each subsequent plant easier to plan and operate.
Most utilities in the Midwest defaulted to coal, which was abundant and could be built faster. ComEd acknowledged this too, choosing coal for some additions when peak load growth demanded speed. But the company’s long-term strategy leaned heavily nuclear, and Illinois’ regulatory environment didn’t stand in the way. The result was a building spree through the 1970s and 1980s that produced the six-site, 11-reactor fleet still running today.
Geography That Made It Possible
Nuclear reactors need enormous amounts of water for cooling, and Illinois has it. The state sits at the intersection of major river systems, including the Illinois, Mississippi, and Rock rivers, along with access to Lake Michigan. Each of the six nuclear sites in the state, Braidwood, Byron, Clinton, Dresden, LaSalle, and Quad Cities, was positioned near reliable water sources. Flat terrain and relatively low seismic risk also made siting easier compared to states with mountainous geography or earthquake concerns.
Illinois’ central location in the Midwest grid mattered too. The state’s nuclear plants don’t just serve Illinois. They feed into a regional transmission network, making the state an electricity exporter. Dense population centers like Chicago created strong baseload demand, and nuclear plants excel at providing steady, around-the-clock power.
The Fleet’s Scale Today
All 11 reactors are now operated by Constellation Energy across the six sites. Together they produce 11,864 net megawatts of electric capacity, more than any other state. Pennsylvania ranks second with 9,346 net megawatts. Illinois’ nuclear output accounts for roughly 54% of the state’s total electricity generation, with fossil fuels contributing about 31% and renewables (mostly wind) making up the remaining 15%.
The economic footprint is substantial. A Brattle Group analysis found that just four of the plants (Braidwood, Byron, Dresden, and LaSalle) contribute approximately $3.5 billion annually to the state’s GDP, support over 28,000 direct and secondary jobs, and generate an estimated $149 million in state tax revenue each year. The plants directly employ about 3,273 workers, with thousands more in supporting industries.
How the State Fought to Keep Them
Having the plants and keeping them are two different problems. By the late 2010s, cheap natural gas had driven wholesale electricity prices so low that several Illinois reactors were losing money. Byron and Dresden were both scheduled to begin shutdown proceedings. Closing them would have eliminated thousands of jobs and, more critically, wiped out the majority of the state’s carbon-free electricity overnight.
In September 2021, Governor J.B. Pritzker signed the Climate and Equitable Jobs Act, which committed nearly $700 million over five years to keep the struggling Constellation plants running. The law also set Illinois on a path to 100% carbon-free electricity by 2045, making it the first Midwest state with that requirement. Reaching that target without the nuclear fleet would be essentially impossible in the near term, since nuclear provides more than three times the carbon-free electricity that wind and solar currently deliver in the state combined.
Licensed to Run for Decades
The fleet isn’t winding down. The Nuclear Regulatory Commission recently renewed operating licenses for multiple Illinois plants, extending their permitted lifespans significantly. Dresden Units 2 and 3 are now licensed through December 2049 and January 2051, respectively. Clinton’s license runs through April 2047. These extensions mean Illinois’ nuclear dominance is locked in for at least another two decades, barring economic shocks or major policy shifts.
The combination that built Illinois’ nuclear fleet, an ambitious utility willing to move first, favorable geography, steady demand from a large population, and political willingness to support the industry, is unusual. Other states had one or two of these factors. Illinois had all of them at the right time, and the infrastructure that resulted has proven durable enough to anchor the state’s energy system well into the middle of the century.