UIL Holdings Corporation
UIL Holdings Corporation was a New England energy-delivery holding company that owned electric and natural-gas utilities before merging with Iberdrola USA to form Avangrid in 2015.
Last updated August 26, 2026
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Overview
UIL Holdings Corporation was a United States energy-delivery holding company created in 2000 during Connecticut's transition to a deregulated electricity market. It served as the corporate parent of The United Illuminating Company, an electric transmission and distribution utility, and later expanded into natural-gas distribution through Connecticut Natural Gas Corporation, The Southern Connecticut Gas Company, and The Berkshire Gas Company. These operating companies had long histories and continued to use their established local names under UIL's ownership. The company was formed as the holding corporation for United Illuminating and United Resources Inc. United Resources had served as the umbrella for UIL's non-regulated businesses, but UIL subsequently sold or exited those activities. By 2006, the group had largely returned its attention to regulated utility operations, reflecting a strategy centered on electricity and gas delivery rather than a diversified portfolio of unrelated energy businesses. UIL's principal electric utility, The United Illuminating Company, supplied and delivered electricity in the Greater New Haven and Bridgeport areas of Connecticut and also provided related energy services. Its gas subsidiaries distributed natural gas to customers in Connecticut, while Berkshire Gas served western Massachusetts. In 2010, UIL agreed to acquire the three gas utilities from Iberdrola USA. Connecticut regulators approved the change of control of the Connecticut gas companies in November 2010, and the transaction was completed on November 16 of that year. The acquisition broadened UIL from an electric utility-centered group into a regional electricity and natural-gas delivery company. Following the gas-utility acquisition, UIL reported service to approximately 690,000 electric and natural-gas customers in 66 communities across Connecticut and Massachusetts and employed roughly 1,850 people in the New England region. Its combined assets exceeded $4 billion according to the company description cited in reference material. The company operated in a highly regulated environment, with state utility commissions overseeing ownership changes, rates, reliability, and other significant aspects of its businesses. UIL's independent corporate existence ended in 2015 when it merged with Iberdrola USA, a subsidiary of Spanish utility group Iberdrola S.A. The combined company was named Avangrid. Iberdrola USA's existing New York utilities, NYSEG and Rochester Gas and Electric, joined UIL's Connecticut and Massachusetts operations within the enlarged group. Avangrid became the surviving publicly traded enterprise, using the New York Stock Exchange ticker AGR. UIL Holdings therefore remains principally significant as the former parent company that assembled a regional New England energy-delivery platform before becoming part of Avangrid.
History
UIL Holdings Corporation emerged from the restructuring of Connecticut's utility sector at the beginning of the state's electricity-deregulation era. Established in 2000, it became the holding company for The United Illuminating Company, commonly known as UI, and United Resources Inc. UI was the regulated electric utility operating in the Greater New Haven and Bridgeport areas. United Resources provided a corporate structure for UIL's non-regulated businesses. The holding-company model allowed UIL to separate its regulated utility activities from other businesses while maintaining a parent organization capable of managing multiple energy-related operations. During the first half of the 2000s, the company disposed of its non-utility interests. By 2006, UIL had substantially refocused its corporate strategy on regulated energy delivery, particularly electric and natural-gas utility operations. A major expansion came in 2010. UIL agreed to purchase three gas utilities from Iberdrola USA: Connecticut Natural Gas Corporation, The Southern Connecticut Gas Company, and The Berkshire Gas Company. The first two served Connecticut customers, while Berkshire Gas operated in western Massachusetts. Because utility ownership changes require regulatory review, the transaction proceeded through state approval processes. Connecticut's Department of Public Utility Control approved the change of control of the Connecticut gas companies in November 2010, and the acquisition closed on November 16, 2010. Massachusetts regulators determined that their approval was not required for the Berkshire Gas portion of the transaction. The acquisition changed UIL's operating profile and geographic reach. Alongside UI's electric business, the three acquired companies gave UIL a portfolio covering both electricity and natural-gas distribution. The combined organization served approximately 690,000 utility customers in 66 communities across Connecticut and Massachusetts and employed approximately 1,858 people. UIL's local operating companies retained their established identities, each having roots extending back more than a century, while UIL provided the parent-company structure and strategic coordination. UIL's final corporate transition occurred in 2015. Iberdrola USA, itself a wholly owned subsidiary of Iberdrola S.A. of Spain, merged with UIL Holdings. The combined company adopted the name Avangrid. Iberdrola USA brought its New York utility businesses, including New York State Electric & Gas and Rochester Gas and Electric, into the enlarged organization. The merger created a broader utility group serving customers across New York and New England. Avangrid became the publicly traded successor, with its shares trading on the New York Stock Exchange under the symbol AGR. As a result of the 2015 merger, UIL Holdings ceased to operate as an independent corporate entity. Its principal legacy is the consolidation of important Connecticut and western Massachusetts electricity and gas-delivery businesses within the Avangrid group.
- 2015
Merger created Avangrid
[1]UIL merged with Iberdrola USA and became part of Avangrid, ending its standalone corporate history.
- 2010
Agreement to acquire three gas utilities
[1]UIL announced its planned acquisition of Connecticut Natural Gas, Southern Connecticut Gas, and Berkshire Gas from Iberdrola USA.
- 2010
Gas-utility acquisition completed
[1]After Connecticut regulatory approval, UIL completed the transaction on November 16, 2010.
- 2006
Return to core utility operations
[1]The company had divested its non-utility businesses and concentrated on regulated energy delivery.
- 2000
UIL Holdings Corporation established
[1]UIL was formed as a holding company for The United Illuminating Company and United Resources Inc. during Connecticut's deregulation period.
Products and positioning
A regulated regional energy-delivery holding company focused on electricity and natural-gas distribution in Connecticut and western Massachusetts.
Electricity transmission and distribution
The United Illuminating Company
The United Illuminating Company was UIL's electric utility subsidiary, serving the Greater New Haven and Bridgeport areas of Connecticut. Its activities centered on the transmission and delivery of electricity, together with related energy services. UI was the principal legacy electric operation within UIL's portfolio and continued as an operating utility after UIL became part of Avangrid.
Natural-gas distribution
Connecticut Natural Gas Corporation
Connecticut Natural Gas Corporation was one of the gas utilities acquired by UIL from Iberdrola USA in 2010. It distributed natural gas to customers in Connecticut and formed part of UIL's expansion from an electric-utility holding company into a combined electric and gas energy-delivery group.
Natural-gas distribution
The Southern Connecticut Gas Company
The Southern Connecticut Gas Company was acquired by UIL in 2010 from Iberdrola USA. It served natural-gas customers in Connecticut and operated alongside UIL's electric subsidiary and other gas utilities under the holding-company structure.
Natural-gas distribution
The Berkshire Gas Company
The Berkshire Gas Company was UIL's Massachusetts natural-gas utility, serving customers in western Massachusetts. It joined UIL's portfolio through the 2010 acquisition from Iberdrola USA and later became part of the Avangrid group.
Brand decisions
2015
Merger with Iberdrola USAM&ABackground
Iberdrola USA owned utilities in New York, while UIL controlled electric and gas delivery businesses in Connecticut and Massachusetts.
Action taken
UIL merged with Iberdrola USA to create the combined utility company Avangrid.
Aftermath
UIL ceased to exist as a standalone company, and the successor group traded on the New York Stock Exchange under AGR.
2010
Acquisition of three Iberdrola USA gas utilitiesM&ABackground
UIL sought to broaden its electric-utility base into natural-gas distribution across Connecticut and western Massachusetts.
Action taken
UIL agreed to acquire Connecticut Natural Gas, Southern Connecticut Gas, and Berkshire Gas from Iberdrola USA; the transaction closed after regulatory review.
Aftermath
The acquisition created a regional energy-delivery company serving approximately 690,000 customers in 66 communities across two states.
2006
Refocus on regulated utilitiesStrategyBackground
UIL had operated with regulated and non-regulated business units after its formation.
Action taken
The company divested its non-utility businesses and returned its strategic focus to core utility operations.
Aftermath
UIL concentrated on electricity and natural-gas delivery before expanding its gas portfolio in 2010.
Recent events
- 2015
UIL Holdings merged with Iberdrola USA to form Avangrid[1]
M&A · Leadership change
UIL Holdings combined with Iberdrola USA, creating Avangrid and ending UIL's existence as a standalone company. The enlarged group included utility operations in New York and New England and traded on the New York Stock Exchange as AGR.
- 2010
UIL agreed to acquire three Iberdrola USA gas utilities[1]
M&A
UIL and Iberdrola USA announced an agreement under which UIL would acquire Connecticut Natural Gas, The Southern Connecticut Gas Company, and The Berkshire Gas Company.
- 2010
Connecticut approved the change of control of the gas utilities[1]
M&A · Regulation
Connecticut's Department of Public Utility Control approved UIL's acquisition of the Connecticut gas companies, and the transaction closed on November 16, 2010.
- 2006
UIL refocused on regulated utility operations[1]
Other
After divesting its non-utility businesses, UIL concentrated its activities on its core regulated electric and gas utility operations.
- 2000
UIL Holdings formed as a utility holding company[1]
Other
UIL Holdings Corporation was established after Connecticut embraced electricity deregulation, becoming the holding company for The United Illuminating Company and United Resources Inc.
Sources1 sources
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