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

Auburn
Bangor
Cape Elizabeth
Dover Foxcroft
Ellsworth
Falmouth
Gorham
Hampden
Island Falls
Jay
Kennebunk
Lewiston
Madison
New Gloucester
Orono
Portland
Quimby
Rockland
South Portland
Topsham
Union
Van Buren
Westbrook
(no X)
Yarmouth
(no Z)