The alphamegalog of the cities of Montana lists the largest city in Montana for each letter of the alphabet. In this case, ‘largest’ is based on population within the city proper.

Anaconda
Billings
Columbia Falls
Dillon
Evergreen
Four Corners
Great Falls
Helena
Inverness
Joliet
Kalispell
Livingston
Missoula
North Browning
Orchard Homes
Polson
(no Q)
Red Lodge
Sidney
Three Forks
Ulm
Victor
Whitefish
(no X)
Yaak
Zortman