I am not sure there is a "free" day at anytime, if you do not live in the Metropolitan area.
I do not live in New York and do not know, but I believe I recall a day you could come and make a donation for entry. I am aure you could dind your information online.
Don't think it is free to anyone anymore, if you are a member, it's free, if you are a New Yorker, you can pay whatever amount you choose. If you are a tourist, you need to pay
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