American dams in the 19th century

To appreciate how essential dams were in the nineteenth century, simply look at the 1840 U.S. Census: It found that almost every river had a dam, and many rivers had dozens.  In total, the twenty-six states that made up the United States at the time had around 65,000 dams.  With a population of only 17 million at that time, the United States had one dam for every 261 people.

That is from the new and often quite interesting Martin Doyle, The Source: How Rivers Made America and America Remade its Rivers.