现在的美国合众银行是经过一系列合并发展而来的，开始于1999年在俄亥俄，Firstar公司（前First Wisconsin国际银行）与Cincinnati的Star银行（前第一国际Cincinnati）的合并。 Five months later, Firstar acquired Mercantile Bancorporation of St. Louis, Missouri. The final major acquisition was Firstar's buyout of U.S. Bancorp, headquartered in Minneapolis, Minnesota. That buyout was completed on February 27, 2001. Firstar changed its name to U.S. Bancorp at that time.
The original U.S. Bancorp was the successor of the United States National Bank of Portland, which was founded in Portland, Oregon in 1891 and changed its name to the United States National Bank of Oregon in 1964. That corporation was acquired in 1997 by First Bank System, Inc., which had its headquarters in Minneapolis, Minnesota. With that acquisition, First Bank System changed its name to U.S. Bancorp. First Bank System was the successor of a bank holding company formed in 1929 by several banks in the Upper Midwest, most notably the First National Bank of Minneapolis and the First National Bank of St. Paul, both of which had been founded in 1864.
In early June 1999, Minnesota Attorney General Mike Hatch filed a lawsuit against Minneapolis-based U.S. Bancorp, alleging that the bank illegally released private customer information to a telemarketer.
Several other banks were acquired by U.S Bancorp's legacy companies. Other banks that were bought by Firstar include Banks of Iowa, Federated Bank, First Colonial Bankshares Corporation, and Investors Bank. Banks bought by Mercantile Bancorporation include Mark Twain Bancshares, Firstbank of Illinois, Hawkeye Bancorporation, and Ameribanc. Star Bank Corporation bought Great Financial Bank, and US Bancorp bought West One Bancorp and WestStar Bank