I've found good detail historic maps for the US at
http://memory.loc.gov/ammem/pmhtml/panmap.html
Same site also has some Canadian maps.

I Googled extensively to find what I wanted.

Edit: don't forget that you may need a map of Austria or the Austria-Hungary empire, or even France, depending on when your family lived in the area.

2nd edit to remove a link which seems to be in violation.