What is the largest denomination of US bills?

The largest current denomination is $100 USD. Although larger bills ($500, $1000, $5000, $10000) were issued in the past they are no longer printed and are destroyed by the Treasury when redeemed at a bank.

The largest denomination of currency ever printed by the Bureau of Engraving and Printing (BEP) was the $100,000 Series 1934 Gold Certificate, designed to simplify transactions between Federal Reserve Banks. They were not circulated among the general public. Since 1969, the largest denomination in active circulation is the $100 bill.

Production of large circulating bills stopped in 1945, and in 1969 the government decided to cease distributing them altogether. The big bills are still around (though mostly in the hands of collectors). They've never been formally recalled but instead are returned to the Treasury if redeemed at a bank. They technically remain legal tender and could be spent, although doing so would be foolish because they're worth much more than face value on the collectibles market.

The biggest bill still in use is the classic C note -- the $100 bill. The "Benjamin" (named because it carries a picture of Benjamin Franklin) was the highest note to survive the 1969 repeal, because by that point, electronic money transfer systems had rendered large paper bills mostly unnecessary.