What was the largest denomination of Federal Reserves Notes ever printed?

$10,000. The bills were printed in small quantities from 1918 to 1945, although they only carried 3 "series" dates - 1918, 1928, and 1934.

More$5000, $1000, and $500 Federal Reserve Notes were also printed up till 1945 but again the last ones were all dated 1934. In 1969 the government halted distribution of bills higher than $100 in an attempt to discourage organized crime. Those denominations were never formally recalled but the bills effectively disappeared from circulation within a few years.

The highest-value US bill ever printed was a $100,000 Gold Certificate issued in 1934 and 1935. They were only used for funds transfers between government departments. None were put into circulation and it's illegal for private collectors to own any of them.