From Q42018 numbers posted on airliners from DOT data...top 10 unserved airports, assuming this includes Domestic only, with PDEW numbers:
San Antonio, 192
Louisville, 130
Memphis, 118
Albuquerque, 116
Omaha, 92
Madison, 89
Tucson, 87
Oklahoma City, 85
Grand Rapids, 85
Birmingham AL, 84
Same...