toruńczyk -who lives in Toruń
It's Torunianin (single) and Torunianie (plural)
As Ziemowit says, forms with '-ak' ending are less formal, but don't apply to all cities. So you don't say 'torunczyk' or 'gdanszczak'; you say 'gdanszczanin/torunianin etc and general rule is creating the names by adding '(n)in'.
Krakowiak, Warszawiak, even Wroclawiak are ok tho.
The naming rule can be split in 3 basic sections:
-naming citizens of Polish cities
-naming foreigners (such as Amerykanin, Brytyjczyk, Norweg, Szwed etc)
-naming citizens of foreign cities( berlinczyk, londynczyk, BUT prazanka= female citizen of Prague (m. - prazanin), and paryzanin = citizen of Paris (f. - paryzanka)
But as you can see - there seem to be no strict rule for foreign cities' citizens :)
I recommend this: