Depends what your definition of 'folk' is. There are many definitions on this forum. Most of the previous posters are going by a definition coined in 1954, but the media might argue with that, and the 'folk' themselves don't use this definition. Have a look at the 'folk' section in HMV. If Mumfords can do it so can you.

A folk song is nowadays anything sung by a folksinger! Are you a folksinger? Hee hee!