Private company
Who owns ATC Holdco LLC
2 companies in the researched set disclose a stake in ATC Holdco LLC, worth $23m between them. ATC Holdco LLC is private, so no 13F reports it: a 13F covers exchange listed positions only. These figures exist because each holder disclosed the stake in its own filings.
What this is
An investment vehicle formed in December 2016 by the owners of American Transmission Company to put money into electric transmission projects outside ATC's traditional Wisconsin and upper Midwest footprint, with a four member board and no operations of its own, and it is described nowhere in public except in the annual reports of the utility holding companies that own it.
The disclosed stakes
One row per position. Where a holder reports the same company in two share classes, both rows are shown rather than summed, because the class is part of a position's identity.
Where each figure comes from
A private stake has no ownership form behind it, so the source is always the holder's own filing or disclosure. Anything modelled says so, with the arithmetic.
- WEC Energy Group, Inc., as of 30 Jun 2026. Q2 2026 10-Q Note 19: 'At June 30, 2026 and December 31, 2025, our equity investment in ATC Holdco was $22.6 million and $23.5 million, respectively, which approximates our maximum exposure to loss as a result of our involvement with ATC Holdco.' ATC Holdco was formed in December 2016 to invest in transmission-related projects outside ATC's traditional footprint; same VIE / equity-method rationale as ATC (limited voting rights). Not publicly traded; 75% is an ownership interest, not a share count, so shares stays null. source
- Alliant Energy Corporation. Same combined 'ATC Holdings' balance as the ATC row above ($501m at 30 Jun 2026, $463m at 31 Dec 2025); the 10-K does not split the carrying value between the direct ATC interest and this ATC Holdco interest, so value_usd is null here too. ATC Holdco LLC itself holds an interest in Duke-American Transmission Company, LLC, which in turn holds only a note receivable related to previously owned electric transmission infrastructure in North America (not an operating business), per the 10-K text; this third-tier indirect interest is too attenuated and undisclosed in size to warrant its own row. sourcesource 2
What this page is not
It is not a complete register. It lists the holders who happen to be inside the researched set and disclosed the stake themselves. A private company can have many other shareholders, and nothing here rules them out: venture investors, founders and employees usually appear in no public filing at all. Percentages are of ATC Holdco LLC where a holder stated one, and are missing where no holder did.