How can I tell if buttercup squash is ripe. I just picked one and it was not ripe. I live in Minnesota :o Eva

This is a rather late response but I just found this site.
Butternut takes a full growing season in your area about 110 days of frost free growing. I have had years in southern Maine when they did not reach maturity before the frost got them but with global warming I've started to grow them again. Had a great crop this year.
If you had a long growing season and could keep the vines from dying from a deseas, they can be harvested when they are a buff tan color. If there is a green tinge to them, they are not ripe.

Sorry, you said buttercup. Pretty much the same answer except for the color and the days to maturity are only 95. Still, they need the full season. Hard to tell when they are ripe other than they have reached full size. By the way, you might want to try Kabocha squash, like buttercup but a bright orang skin that makes it easier to tell it is ripe.