State dental board with a little work. Do a liscense search for the area you are interested , get the population numbers from the net. A little math and you have you population to dentist ratio. Be aware that if corporate chains are present in the area of interest they usually list every dentist that may possibly be at that location even if it's one a month. For instance the local corporate oral surgery practice lists nine names for my location but in reality only one of them practices in Marion.