How long does it take for mail to get to US from different parts of Europe?

It really depends how how you send it. For instance, I sent few postcards to Illinois and Texas, by planes, and it took good two weeks until the person in Illinois got it and another week or two till the person in Texas got it. If you send it by boat however, it will take much much longer, I tried it as well, and it arrived after a month and a half later... So from wherever you send it, make sure the card or letter is marked that it will go by plane! Good Luck!