What year did the US stop printing 1000 dollar bills?

The last printing was in 1945. However these bills were issued as part of the 1934 series and they carried the series date 1934 A.

It was still possible to request them from a bank up till 1969. That year President Nixon suspended distribution of all bills larger than $100 in an effort to reduce money-laundering and other criminal activities. Large bills are technically still legal to spend but they're worth more to collectors.