Question: I wish to use the following sentence as the comment on a form field. I have already come up with a short-form label for the field. This text is meant to explain the field in a bit more detail:

**The country [where] you come from.**

The question is: is this "where" needed there, can be used there (optional) or cannot be used there (error).

As English is not my mother language, sometimes these things come up. Please don't be hard on me.

EDIT: I'm somewhat overwhelmed by the answers and appearing complexity of the issue. Yes, I have an input field and I wish to write a label to it. We all know the basic phrases like "I come from Australia" - "Where do you come from?". Cannot it be turned around in the form like "The country you come from"? 

And if the following would be correct: "The country I live **in**"? Or I may only put the preposition to the end if it's not an independent clause but a subordinate one (terms may not be correct, forgot them): I've returned to the country I live **in**.

Answer: 
Formally it would be "the city from which you came", "the city whence you came" (except that 'whence' is definitely archaic), "your native city", or perhaps "your city of origin" or "original city".

Colloquially, in a sentence I would say "The city you came from" instead of "The city where you came from". If I were writing it though, e.g. on a form to label an input text field, then "The city where you came from" might be better because it's a little less ambiguous.

Note that neither is entirely grammatical though, because they're not complete sentences: they're missing a subject and a verb.
I believe the way you have it is correct - "where" is optional.