Twenty Equal Banks: The Size Distribution of 4,212 US Banks in June 2026, a Pareto Tail with Exponent below One, and an Exact Link between Concentration and the Number of Banks

Using FDIC data on the 4,212 active insured institutions with positive assets (mostly reporting for 30 June 2026), I describe the size distribution of US banks. Total assets are 26,452.7 billion dollars; the largest bank holds 15.47%, the top four 40.19% and the top ten 54.21%, while the median bank has 0.388 billion dollars. The Herfindahl-Hirschman index of assets is 501.9, equivalent to 19.9 banks of equal size. I prove and verify the identity HHI = 1/n + n Var(s), which separates the effect of the number of banks from the inequality of their shares. The upper tail is close to Pareto with an exponent below one: the Hill estimator gives 0.736 to 0.792 across tail sizes of 50 to 1,000 banks, and the Gabaix-Ibragimov rank-minus-one-half regression gives 0.762 to 0.876. An exponent below one implies that the largest bank holds a non-vanishing share of total assets however many banks there are. The number of insured institutions fell from a peak of 14,496 in 1984 to 4,327 in 2025, a fall of 70.2%. Under the identity, consolidation raises measured concentration through both terms.