In which department is situated such city ?

In some web-sites you have to fill a form and you must know the name and the code of the department (or subregion) where your ancestors lived. But you just know the city.
There are many ways to find the information. Among  them, you can try  a very good site designed by Sylvain Chardon http://perso.wanadoo.fr/sylvain.chardon/locom/

Here are some explanations to use this site.

When you click on the picture you get this

You have to select "Acces aux communes", on the right.

 

You have to indicate the first 2 letters of the name of the place and click on the "Acces au fichier" button. For example you can search "Freistroff"

Then you get this and you can select the name of the place you're looking for.
When you select a place a spot highlights on the map.

The last line is the department : its name and code (2 digit numbers).
Here the department code is 57, which refers to Moselle.

There are many other things very interesting in this site and I let you discover it.
Unfortunately it's only in French.