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TerraWatt wants to turn Illinois' shuttered 381-acre Alton Steel mill into a data center starting at 200 MW, but rezoning and an Ameren Illinois study decide how much power it can ever draw.
2 min readAI-assisted
TerraWatt's own rendering of its proposed Riverbend Technology Center. It is an illustration from the developer's project site, not a photo of the Alton Steel site.
Image: TerraWatt
Source · Rendering from TerraWatt's official Riverbend Technology Center site, used for news reporting.
TerraWatt, the St. Louis developer behind the Armory data center, has proposed an Alton Steel data center campus of up to 1 GW on the 381-acre former mill site in Alton, Illinois, starting with one 200 MW block, according to St. Louis Magazine and St. Louis Public Radio.
The project, called Riverbend Technology Center, would be built in 200 MW increments. St. Louis Magazine reports that TerraWatt puts the cost of each block at $2.64 billion, while St. Louis Public Radio cites a $3 billion project figure from the company's release. TerraWatt has a contingent agreement to buy the mill site at 5 Cut Street from Alton Steel Inc., which stopped production in January 2026, and says it would close in 2027.
TerraWatt's first 200 MW block sits just above the mill's draw of about 160 MW; the 1,000 MW campus is a ceiling, according to St. Louis Magazine.
Illustration (AI-generated)
The sale depends on Alton rezoning the site, on a study by Ameren Illinois, and on TerraWatt's own due diligence. Cecilia Dvorak, a consultant representing TerraWatt, told St. Louis Magazine that 200 MW is about what the company expects Ameren to deliver in the short term, because the mill drew about 160 MW. She said the full buildout is still open, a "chicken and egg" question that depends on what the utility can supply.
That makes the 1 GW figure a ceiling, not a plan. Only the first 200 MW block is tied to the site's existing electrical connection, and each further block would need its own utility answer. The company also points to rail, roads and an on-site wastewater treatment facility already at the mill.
TerraWatt estimates a 200 MW data center would use about 400,000 gallons of water a year, against 177.7 million gallons for the steel mill, according to St. Louis Magazine. The company says each block would bring about $17.2 million a year in new property taxes, and that it will seek no local tax incentives or public money, including from the Riverfront tax-increment financing district the site lies in. These are the developer's estimates and have not been independently verified.
The first phase would be demolishing the 1.26 million square feet of mill buildings, followed by cleanup of the site. Dvorak said the cleanup is likely to involve regulated materials, TerraWatt intends to fund it, and the cost is not yet known because a 2023 environmental assessment needs updating.
Alton is TerraWatt's second proposal in the St. Louis region. The company is also planning a 120 MW data center in Midtown St. Louis, which St. Louis Public Radio reports is expected to start construction in August 2027. TerraWatt is suing St. Louis over the renewable-energy conditions placed on that project, and another suit aiming to halt it is pending. Voltgrid has also covered another steelworks conversion, Era4's 1 GW Newport plan.
No formal permit or rezoning application has been filed, according to Alton Mayor David Goins, who said the city expects clear answers and plans to hire an independent consultant. Alton Steel's board and leadership back the plan, but its chief executive, Chris Ervin, called it "not a done deal." Local residents are split, with some welcoming reuse of the idle site and others raising water, noise and rezoning concerns, First Alert 4 reported. TerraWatt is holding an open house at The Wedge, 620 E. Broadway, on Tuesday, Oct. 27, from 6 p.m. to 7:30 p.m.
