In 1928, Amadeo Giannini, born in California to Italian immigrant parents, formed a holding company, the Transamerica Corporation, to consolidate his existing financial ventures, which began business with $1.1 billion in assets and both banking and non-banking activities.

From the 1930s through the mid-1950s, Transamerica made a number of acquisitions of banks and other financial corporations throughout the western United States, creating the framework for the later First Interstate system.

[6] First Interstate ran into its own troubles in the late 1980s and early 1990s stemming from bad real estate loans and the severe recession in California.

Rumors of a takeover of First Interstate were rife in the early 1990s before the bank recovered fully by mid-decade under the leadership of Chairman and CEO Edward M. Carson (1929–2010).

The latter made a serious bid for First Interstate, with the two banks reaching a formal merger agreement in November valued initially at $10.3 billion.

The current First Interstate BancSystem continues to operate 306 locations in 14 states as of 2023 in chiefly the northern Great Plains and Rocky Mountain regions.

[13] In June 1986, a highly trained group, called the "Hole in the Ground" crew by the media, tunneled under the First Interstate Bank in Hollywood at Spaulding Avenue and Sunset Boulevard through an extensive network of tunnels over the course of several months and took about US$270,000 (equivalent to $750,000 in 2023) in cash and the contents of 36 safe deposit boxes valued at US$2,500,000 (equivalent to $6,900,000 in 2023).

The group rode all-terrain vehicles through the underground storm drain system of Los Angeles, and used gas-powered generators, hammer drills, power saws, and digging equipment to tunnel 100 ft (30 m) up into the bank's vault.

[14][15] On January 24, 1992, four robbers wearing boiler suits and ski mask and brandishing AK-47s broke into the Interstate Bank in Victorville across the street from the mall.

Two hours after the robbery the police arrested Gerry Edward Alexander, getaway driver Jon Harrington, and robbers Anthony Hicks and Willie Harris.