MISO Awards Ameren-Led Consortium Two 765-kV Illinois Lines Totaling $1.66 Billion, 237 Miles
- Capacity & Wholesale Markets News Policy & Markets
Marin Holt
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- Total investment: $1.658 billion
- Voltage: 765 kV
- New transmission line: 237 miles
- Expected in-service: 2034
The Midcontinent Independent System Operator (MISO) on May 19, 2026 selected a consortium led by Ameren Transmission Company of Illinois (ATXI) and GridLiance Heartland to build two 765-kilovolt transmission projects across Illinois, together 237 miles of new line, a new 765/345-kV substation, and an estimated $1.658 billion investment. Dairyland Power Cooperative and the Illinois Municipal Electric Agency (IMEA) hold minority stakes. Both projects are scheduled to reach service in 2034.
The Two Projects
The larger project, Sub T–Iowa/Illinois State Line–Woodford County (STIW), covers roughly 149 miles of new 765-kV line at an estimated $940 million. The second, Woodford County–Illinois/Indiana State Line (WIIL), adds 88 miles of 765-kV line plus a new 765/345-kV substation for an estimated $718 million. Both stem from MISO’s Long Range Transmission Planning Tranche 2.1 portfolio, approved in December 2024 to relieve congestion and carry load growth across the Midwest.
Ownership and Roles
ATXI and GridLiance Heartland each hold 43 percent of the projects and lead development, engineering, and construction. Dairyland Power Cooperative takes 11 percent and IMEA 3 percent, with both cooperatives owning their shares once the lines enter service. GridLiance is a NextEra Energy Transmission company; NextEra Energy Transmission president Matt Valle called the lines “critical to building a stronger, more resilient transmission backbone for the Midwest.”
Critical Perspective
MISO’s award commits an estimated $1.658 billion for 237 miles of new 765-kV line across Illinois, with service targeted for 2034. That eight-year horizon assumes routing and right-of-way clear on schedule, the exact stage where large transmission projects tend to stall rather than in the engineering. The SunZia line from New Mexico to Arizona spent roughly seventeen years in permitting and litigation before construction finally began in 2023, and the New England Clean Energy Connect was halted mid-build by a 2021 Maine referendum. If the load growth from data centers and electrification is a problem grid operators say they face now, what carries the Midwest until 2034, and who absorbs the congestion cost if the date slips again?
Why It Matters
A 765-kV line moves several times the power of the 345-kV circuits that dominate the Midwest, so fewer new corridors carry the load growth from data centers, electrification, and new generation. For Illinois ratepayers, MISO spreads most of the cost across its multi-state footprint rather than onto local customers alone. The harder question is timing: with service set for 2034, the backbone answers demand that grid operators are forecasting now, and any slip in permitting or right-of-way pushes relief further out.
Sources
- Ameren: MISO selects consortium to deliver Illinois grid projects (May 19, 2026)
- Illinois Business Journal: MISO selects consortium (May 19, 2026)
- PR Newswire: MISO consortium selection (May 19, 2026)
