Вы можете использовать groupby, а затем получить размер каждой группы:
dfexcel.groupby(['State','Issuing Agency']).size()
Вывод:
State Issuing Agency
NY CON RAIL 2
DEPARTMENT OF SANITATION 2457
DEPARTMENT OF TRANSPORTATION 22065
FIRE DEPARTMENT 8
HOUSING AUTHORITY 2
NYC TRANSIT AUTHORITY MANAGERS 6
NYS OFFICE OF MENTAL HEALTH POLICE 2
OTHER/UNKNOWN AGENCIES 239
PARKS DEPARTMENT 54
POLICE DEPARTMENT 10340
PORT AUTHORITY 5
TRAFFIC 26344
OH DEPARTMENT OF SANITATION 7
DEPARTMENT OF TRANSPORTATION 47
PARKS DEPARTMENT 1
POLICE DEPARTMENT 13
TRAFFIC 35