When you enter your W-2G into the program, there will be a blue Locality link next to Box 18(Please see screenshot below). When you click on the link it will provide a list of Locality ID codes by state.
If you are unable to locate the Locality link, I have provided a list of all the locality codes supported by TurboTax. If your locality is not listed or if the payment is for two or more localities you will use the code XXX instead.
Kentucky Locality Codes
LEX - Lexington
LOU - Louisville
Michigan Locality Codes
ALB - Albion
BCK - Battle Creek
BRR - Big Rapids
DET - Detroit
FLT - Flint
GRR - Grand Rapids
GRA - Grayling
HAM - Hamtramck
HPK - Highland Park
HUD - Hudson
ION - Ionia
JAC - Jackson
LNS - Lansing
LPR - Lapeer
MHT - Muskegon Heights
MKG - Muskegon
PNT - Pontiac
PHN - Port Huron
POR - Portland
SAG - Saginaw
SPR - Springfield
WAL - Walker
Missouri Locality Codes
SL - St Louis
KC - Kansas City
New York Locality Codes
NYC - New York City, New York
YON - Yonkers, New York
Ohio City Codes
MR - RITA Municipal Tax
SDR - (four digit school district)
CCA - CCA Municipal Tax
ECC - CCA City Tax Form, Employment Tax Estimate
RCC - CCA City Tax Form, Residence Tax Estimate
Oregon Locality Codes
MUL - Multnomah, Oregon
Screenshot