A four-company consortium has been selected by MISO to build 237 miles of new 765-kilovolt transmission lines across Illinois — two separate projects stretching from the Iowa border to the Indiana state line, with a combined estimated cost of $1.66 billion.
The assignment, awarded to Ameren, GridLiance, Dairyland Power Cooperative, and the Illinois Municipal Electric Agency, targets an in-service date of 2034. At that scale, it represents one of the most significant grid infrastructure commitments the Midwest has seen in years.
A consortium built for scale
The four partners bring genuinely different institutional identities. ATXI — Ameren Transmission Company of Illinois — is a rate-regulated utility subsidiary based in St. Louis. GridLiance Heartland is a subsidiary of NextEra Energy Transmission, operating as a competitive transmission company. Dairyland Power Cooperative is a wholesale electricity provider headquartered in La Crosse, Wisconsin, while IMEA, the Illinois Municipal Electric Agency, is a not-for-profit unit of local government representing municipal electric systems statewide. Ownership stakes are 43%, 43%, 11%, and 3%, respectively.
The structure distinguishes between developers and owners. ATXI and GridLiance will lead development, construction, and operation of both projects from the outset. Dairyland and IMEA, by contrast, assume their ownership portions once the projects enter service — a model that lets smaller organizations participate in major infrastructure without bearing full development risk.
That institutional mix is part of what makes this arrangement worth noting. An investor-owned utility subsidiary, a competitive transmission developer, a generation-and-transmission cooperative, and a municipal agency rarely share a project at this scale. Large transmission builds increasingly require assembling multiple entity types to spread cost, risk, and stakeholder reach across a broader base.
Two projects, one backbone
The two projects are geographically distinct but designed to function as a continuous system. The STIW project — Sub T Iowa/Illinois State Line to Woodford County — involves constructing two new 765-kV lines spanning approximately 149 miles. One line runs from the Woodford County Substation westward to the Iowa/Illinois state line; the other continues west into Iowa toward the Sub T Substation. MISO estimates the STIW project at $940 million.
The WIIL project — Woodford County to the Illinois/Indiana State Line — covers 88 miles moving east and northeast from the same Woodford County hub. It includes two new 765-kV lines and a new 765/345-kV substation. One line runs east toward the Indiana border; the other runs northeast for roughly 1.5 miles before interconnecting with a separate 765-kV segment. MISO’s estimated cost is $718 million.
Together, the two projects create a 765-kV corridor stretching from Iowa through central Illinois to Indiana, with Woodford County as the node connecting both directions. Both STIW and WIIL are competitive projects within MISO’s Long Range Transmission Planning Tranche 2.1 Portfolio, approved in December 2024.
Why 765-kV lines matter
Voltage level isn’t a technical footnote — it shapes what a transmission line can actually do. At 765 kilovolts, these lines operate at among the highest voltage levels used in North American grids. Higher voltage means electricity travels longer distances with proportionally lower energy losses, and a single line carries significantly more power than lower-voltage alternatives.
That capacity has concrete implications for the broader grid. High-voltage backbone lines reduce congestion, improve reliability during peak demand or outage events, and make it easier to move power from generation sources to population centers — including renewable generation located far from where it’s consumed.
The Midwest context adds urgency. Electricity demand across the region is rising, driven by data centers, industrial electrification, and large new loads that weren’t part of grid planning assumptions even a decade ago. Building backbone infrastructure now is, in part, a calculated bet that the grid will need to carry substantially more power by the time these lines come online.
The road to 2034
Both projects carry an expected in-service date of 2034 — but that target depends on completing a substantial sequence of steps first. Regulatory review, permitting, community and stakeholder engagement, and multi-state coordination all lie ahead before construction can begin in earnest.
The organizations involved bring meaningful reach to that process. ATXI operates within Ameren’s service territory, covering 2.5 million electric customers across Illinois and Missouri. NextEra Energy Transmission operates more than 3,200 miles of transmission lines across 19 states and Canada. Dairyland serves over 800,000 people across a four-state area through 24 distribution cooperatives and 27 municipal utilities, and IMEA represents 32 municipal electric systems in Illinois.
That footprint means existing relationships with regulators, communities, and local contractors across the affected region — relationships that will matter as both projects move through the approval process. How efficiently those engagements proceed will likely determine whether 2034 holds as a realistic target or slips under the weight of regulatory complexity. For now, the selection marks the formal start of a long infrastructure cycle that the Midwest grid is counting on to deliver.
