I was about to correct a line like "Townville located in east Blaze County has grown rapidly since 2000 and continues to do so." to "Townville, located in east Blaze County, has grown rapidly since 2000 and continues to do so.", but I wasn't certain that I was right. I also didn't know what reference I might use to find out.
This would be correct. Using commas in this way is the same as using "(" and ")" in order to denote extra information. A way to check for correct usage is to remove the subordinate clause and check for intelligibility. i.e. does the sentence still make sense?
A useful source for this information is the book: Eats, shoots and leaves.