Pennsylvania, Indiana, Kentucky and Wisconsin have already joined the Illinois FutureGen coalition, with Ohio jumping aboard because of the high potential for transferability of the project's technology.
The towns of Tuscola and Mattoon are both vying for the chance to call the first zero-emissions coal-fired facility home, and are up against Jewett and Odessa, Texas.
State Governor Ted Strickland stressed the significance of choosing one of Illinois' host sites in a letter to the FutureGen Alliance, noting its benefits can extend to other neighbouring coal states, including Ohio.
"I believe it is essential to site both the FutureGen power plant and its carbon capture and sequestration pilot project in a location that maximises the value of this significant federal investment to the entire nation. And I believe that place is Illinois," he said.
"Illinois has the right combination of geology, expertise and transportation infrastructure, all strengthened by state and community support.
"More importantly, the characteristics of the Illinois sites have much more in common with those of coal producing states with a significant portion of the nation's power plant fleet - both the challenges and lessons learned at Illinois sites will translate more quickly in Ohio."
According to the Energy Information Administration, Ohio mined 22.7 million tons of coal last year and received 87% of its electricity from coal.
Illinois Governor Rod Blagojevich thanked Strickland for his endorsement.
"It's important to note that states that produce and consume coal are paying close attention to this competition," he said.
"It is vital that this project is placed in a location that offers the best opportunity to replicate FutureGen's technology."
The FutureGen Industrial Alliance is developing the project in conjunction with the US Department of Energy. An announcement on a final site selection is expected in mid-December.
Members of the FutureGen Alliance include American Electric Power, Anglo American, BHP Billiton, the China Huaneng Group, Consol Energy, E.ON US, Foundation Coal, Rio Tinto Energy America, Peabody Energy, PPL Corporation, Southern Company and Xstrata Coal.
FutureGen will produce 275 megawatts of electric power, or enough electricity to power 150,000 homes, as well as hydrogen for fuel-cell technology.