Comparing wealth of individuals across large spans of time is difficult, as the value of money and assets is heavily dependent on the time period. There are various methods of comparing individuals' wealth across time, including using simple inflation-adjusted totals or calculating an individual's wealth as a share of contemporary gross domestic product (GDP). For this reason, there is not one decisive ranking of the richest Americans in history.

Many sources cite John D. Rockefeller (1839–1937) as the richest person in the history of the United States, however this result comes not from adjusting his wealth for inflation, but by comparing his wealth to the size of the American economy at that time. Since the economy was relatively small during his time period, his wealth represented a larger portion of the total economy. For example, economic blogger Scott Sumner noted in 2018 that Rockefeller was worth $1.4 billion when he died in 1937, equivalent to about $24 billion in dollars in 2018 when adjusting for inflation. Meanwhile, Bill Gates in 1999 was worth nearly $150 billion in dollars adjusted to 2018.

The second-richest person in terms of wealth compared to contemporary GDP is a subject of dispute. While most sources attribute this status to Andrew Carnegie, others argue that it could be Bill Gates, Cornelius Vanderbilt I, John Jacob Astor IV, or Henry Ford. Determining the lower ranks is an even more contentious debate. Vanderbilt left a fortune worth $100 million upon his death in 1877, equivalent to $2.4 billion today. As the United States became the world's leading economic power by the late 19th century, the wealthiest people in America were often also the wealthiest people in the world.