English: From the American currency exhibit at the Federal Reserve Bank of San Francisco.

Between 1837 and 1866, a period known as the "Free Banking Era," lax federal and state banking laws permitted virtually anyone to open a bank and issue currency. Paper money was issued by states, cities, counties, private banks, railroads, stores, churches, and individuals. By 1860, an estimated 8,000 different state banks were circulating what were sometimes called "wildcat" or "broken" bank notes.

The term "wildcat bank" referred to the remote locations of some banks, more accessible to wildcats than people. When a bank "went broke," the currency they issued became worthless. The era ended with the passing of the National Bank Act of 1863.