Reporting by Joseph States for Chicago Tribune:
Opponents of the Grayslake T5 data center are focusing on almost 16 acres of wetlands on the site that developers have applied to fill in, seeing it as a potential stopping point for a project that has sparked increasing resistance.
Earlier this year, the developers of T5 @ Chicago IV applied to fill in 15.75 acres of wetlands with the U.S. Army Corps of Engineers. In April, the USACE told T5 that it would issue a 30-day public notice describing the project as happening “in the near future.”
After that period, the letter said a determination would be made whether to issue or deny a permit, noting “delays may result if significant issues need to be resolved.” That notice has not yet been issued.
Barrington-area resident Michael Smith is a co-founder of the Lake County Data Center Opposition Coalition, which is planning to file a lawsuit against the development.
He criticized Grayslake, which has advocated for the development publicly, for allegedly flipping on its “historical position” on wetlands and allowing the destruction of “an important waterway and watershed.”
“You can read it on their website when they talk about their village plans for the future,” Smith said. “This goes totally against what they have traditionally stood for and espoused.”
Based on T5’s application, if its preferred plan were to go through, the wetlands — at least some of which feed into Mill Creek and then the DesPlaines River Watershed — would be permanently filled in. T5 would be required to provide wetland mitigation.
If fully built out, the Grayslake data center could be one of the largest single developments in Lake County’s history, with up to 10 million square feet of data center space potentially planned.
Brian Frank, chief engineer at the Lake County Stormwater Management Commission, said he has not yet been contacted by the USACE regarding the start of the required 30-day public notice. He didn’t have an exact timeline for when that notice period could start, although he knew the applicant’s consultant had requested several months ago that it start as soon as possible.
According to a September 2025 letter from the SMC sharing its findings with T5, at least some of the wetlands on site likely fall under USACE jurisdiction, since they feed into the Des Plaines River. Other portions are “isolated waters of Lake County,” the letter said, meaning they are subject to wetland regulation by the SMC.
However, Frank said earlier this year that jurisdiction was still being determined by the USACE. If the Army Corps determines some or all of the impacted wetlands fall under the county’s jurisdiction, that’s when SMC would step in.
Since a 2023 U.S. Supreme Court decision in Sackett v. EPA, federal protections from the Clean Water Act regarding isolated wetlands have been dropped — although Jennifer Walling, executive director of the Illinois Environmental Council, said Lake County has a fairly robust program for mitigation.
Walling warned that filling in nearly 16 acres of wetland would have significant impacts on drainage and flood control. Wetlands also filter water and provide habitat for wildlife, she said.
“Wetlands are incredibly important, so I am definitely very concerned about the development,” Walling said.