I don’t know if the Town of Leesburg ever had a flag but, Loudon County does.  Here is the history and description of the flag:

http://www.loudoun.gov/Default.aspx?tabid=505

http://www.loudoun.gov/Default.aspx?tabid=553

And an image of the flag, by our own, Joe McMillan can be found here:

http://www.fotw.us/Flags/us-valdn.html

Here is the seal:

http://www.loudoun.gov/Default.aspx?tabid=516

I remember seeing the coat of arms with supporters and crest. I will have to look through my books and scan it.