Us Savings Bonds Information

Question: Where can I find my the date of purchase of a savings bond after I already cashed it in?
I cashed in about 15 bonds two years ago. Unfortunately, I did not copy them. The bank gave me a form with the serial numbers and the total amount paid, but I don’t have the information on each bond. I know some where purchased in the early 1960s and some later, but I would like to have the exact dates. I can’t seem to get it on the US Government treasury site. Any idea how I can find this info?
Answer: the bank will keep a record, which will probably be in their archives and they will charge you a small fee to access them.
1977 “Grasshopper and the Ants” US Savings Bonds Ad Council PSA