That's what I wonder about too. If I'm not wrong, it's should be "Lillaland" gramatically, then it would mean "(the) little land". (Like in "Gamla Stan" which means "(the) old town". Another confusing thing is that they don't use definite form for the place names, even if the noun is definite.)
Because when a noun with an adjective gets definite, the adjective gets the plural form. However, the "liten" word has a different situation. When it is used with a plural noun (definite or indefinite) it becomes "små" (for example "de små flickorna" = the little girls), but when it is used with a singular definite word it becomes "lilla" ("den lilla flickan" = the little girl). So according to that rule, Småland means "(the) little lands". But I don't know why it isn't "Småländer" instead. That's kinda confusing.
Sorry for my poor English, I hope you understand what I mean :D
Småland is a province in Sweden. It originally consisted of 12 different, small regions, "land". You're right that "små" is plural. The plural of "land" as in country is "länder", so in modern Swedish it ought to be either "litet land" or "små länder". However here "land" is used in an older sense, which explains the strange plural. – Even today, the word "land" has another meaning, "garden plot", which has also got the plural "land".
"stan" is a shortened version of "staden" which is used so often that it has become normal and in some contexts even looks better than the long form. You can see some people writing sta'n to make this clear, although that is not recommended.
So it's really
en stad, staden (or stan), flera städer, städerna
There's also an alternative form for the genitive singular: instead of stadens you can write stans.
"liten/lilla" ("lille" is an alternative form for masculine beings) is for singulars and "små" is for plurals. There are a some irregular adjectives in Swedish.
'en liten sko' - 'a small shoe', 'den lilla skon' - 'the small shoe'
'små skor' - 'small shoes', 'de små skorna' - 'the small shoes'