Analysis
NAICS 521 is the 2022 subsector for monetary authorities-central bank, part of 52 (Finance and Insurance).
It has only one more detailed code, 521110, which covers exactly the same activities; the definition, index entries and statistics are on that page.
County Business Patterns counts 66 US establishments in this code in 2023, employing 22,009 people at an average annual payroll of $147,648 per employee (96th percentile of national industries). 8% of the establishments have fewer than five employees, which points to larger operations.
Between 2018 and 2023 the number of establishments grew 14% and employment rose 11%. The 2018 count used NAICS 2017, so part of a large move can come from codes being redefined rather than from businesses opening or closing.
By establishments it ranks 5th of the 5 codes at this level within Finance and Insurance, with 0% of them.
Official definition
The Monetary Authorities-Central Bank subsector groups establishments that engage in performing central banking functions, such as issuing currency, managing the Nation's money supply and international reserves, holding deposits that represent the reserves of other banks and other central banks, and acting as a fiscal agent for the central government.
Source: US Census Bureau, NAICS 2022 Manual.