There were definitely some Brown family in Clonmel in the late 18th century. The Directory of Clonmel 1787 includes an entry
Brown Catherine, Mercer, Main St.
You may wish to consult early trade and postal directories for the area. I suggest a look at Shane Wilson’s Irish directory database at http://www.swilson.info/dirdb.php It is searchable by location and provides links indicating which are online free to view and which are pay to view.