Unitil Energy Systems (UES) is a combination of Concord Electric Company and Exeter & Hampton Electric Company. Concord Electric Company was organized in 1901 and engaged in the purchase, transmission, distribution and sale of electricity to customers in Concord, NH and surrounding towns. Exeter & Hampton Electric Company was organized in 1908 and provided the same services to customers in Exeter and Hampton, NH and surrounding communities. Today, UES provides electric distribution service to more than 72,000 customers in the Capital and Seacoast regions of New Hampshire, serving the 31 communities of Allenstown, Atkinson, Boscawen, Bow, Brentwood, Canterbury, Chichester, Concord, Danville, Derry, Dunbarton, East Kingston, Epsom, Exeter, Greenland, Hampstead, Hampton, Hampton Falls, Hopkinton, Kensington, Kingston, Loudon, Newton, North Hampton, Pembroke, Plaistow, Salisbury, Seabrook, South Hampton, Stratham, and Webster.

Fitchburg Gas and Electric Light Company (FG&E), a Massachusetts corporation organized in 1852, became part of the Unitil system in 1992. FG&E originally manufactured gas to illuminate the gas lights in downtown Fitchburg, but over the years the company expanded its operations to include natural gas and electric service in Fitchburg and a number of surrounding communities. Today, FG&E provides retail electric and natural gas distribution service in a 170-square-mile service area in north-central Massachusetts, with an estimated population of 82,000. This includes electric distribution service to 28,000 customers in the communities of Fitchburg, Townsend, Lunenburg and Ashby, and natural gas distribution service to 15,000 customers in the communities of Fitchburg, Townsend, Lunenburg, Ashby, Westminster and Gardner.

Unitil Resources, Inc. was incorporated in 1993 and, through its subsidiary Usource LLC, provides energy brokerage service to large energy users throughout the Northeast seeking competitive electricity or natural gas supplies.

Unitil Service Corp., incorporated in 1984, provides centralized administrative and management services to Unitil System subsidiaries. Unitil Service Corp. is located at Unitil's corporate headquarters facility in Hampton, New Hampshire, and operates a customer service center in Concord, New Hampshire.