Black Hills Corp. and NorthWestern Energy announced plans this week to merge in an all-stock transaction that will create a regional electric and natural gas utility company with a combined enterprise value of $15.4 billion.

The merged company will serve about 2.1 million customers across eight states, operating approximately 38,000 miles of electric lines and 59,000 miles of natural gas pipelines.

Brian Bird, current CEO of NorthWestern, will lead the combined company. Marne Jones, currently Chief Utility Officer at Black Hills, will serve as COO. The headquarters will remain in Rapid City, with the company continuing operations in South Dakota, Montana, Nebraska, and other areas where both companies already serve.

Officials say the merger will provide a more resilient platform to meet rising energy demands and allow for over $7 billion in infrastructure investments through 2029. It's also expected to be immediately accretive to earnings and support a 5-7% long-term EPS growth rate.

"Together, we will be better positioned to accelerate investment in energy and grid infrastructure," said Brian Bird, calling the merger a win for customers, employees, and shareholders.

Pending shareholder and regulatory approvals--including in South Dakota, Montana, and Nebraska--the deal is expected to close within 12 to 15 months. The combined company's new name and ticker symbol will be announced closer to the closing date.