Board of Trustees notes retention

I am a Trustee on the Board of our library. I also serve as the Secretary to the Board. As such, I do the note-taking and draft the meeting minutes for every board meeting. Do I need to retain my handwritten notes, once I have transcribed them into document format? If so, how long must they be kept and where? FYI, the minutes are drafted, approved by the Board, then uploaded to the library website where they are available to the public.

Thanks for your consideration. Much appreciated.