[2] The ATCO Group of Companies includes the following subsidiaries: Canadian Utilities, with its subsidiaries: ATCO Structures (manufactures, leases, and sells modular buildings;) ATCO Frontec (workforce camp services, operational support, facilities management and disaster response) ATCO was founded in 1947, by S. Don Southern who gave a minority stake to his son Ron Southern, under the name Alberta Trailer Hire, renting fifteen utility trailers in the Calgary area.

By the early 1960s, the company had operations across North America and in Australia.

ATCO Industries Ltd. became a public company in March 1968, with shares traded on the Toronto Stock Exchange.

In 2016, ATCO re-entered the retail energy industry in Alberta as ATCOenergy.

In 2022, ATCO agreed to pay a fine after overcharging for work on a new transmission line.