UI CT’s history began in 1881 with several small lighting companies and was formally established as The United Illuminating Company in 1899. In 2000, UI became a subsidiary of UIL Holdings Corporation to hold regulated and related non-regulated businesses. In 2010, UIL and Iderdrola merged and purchased several local gas providers in Connecticut. Today, the UIL/Iderdrola merger is known as Avangrid and is the parent company of UI.