Yes.
The number of balrogs has changed in Tolkien's mind. In the beginning they were thousands of them, and they were quite weak. For instance when Feanor is surrended by balrogs, Tolkien thought them as far weaker and numerous than in later writings, such as the LotR.
In the end he decided that they were seven of them, with the one in the Moria the very last of them.
In the last version, the Balrogs are maiar who were attracted by Morgoth's power and corrupted by him. So they do not reproduce (only Melian among the maiar did), nor were they created by Morgoth.
Note that we only know the number of balrogs through Christopher Tolkien, who compiled his father's writing. However it's quite obvious when reading the Similarion that they grow stronger. At some earlier versions there are entire armies of balrogs during the attack on Gondolin in the Similarion, which would be ridiculous were there as powerful as shown in Lotr.
All those info come from [Home][1], which is not completely canonical as not approved for publication by Tolkien.
Edit: see Lost Tales, Part II, "The Fall of Gondolin" [1]: http://en.wikipedia.org/wiki/The_History_of_Middle-earth