I don't know what sort of passport you will be travelling on (or where
Montgomery County is, sorry!) - but the following page gives you very
detailed information for Belgium and links to other countries' requirements.
For example, for entry to Belgium: U.S. Passport must be valid 3 months
beyond intended stay.
Hope this gives you a starting point.
Certainly, some countries require that your passport be valid for six months
after your entry date.