It’s so much easier naming people from a certain state. Usually you just add -n or in a few cases, -er. What’s the deal with cities though? Is there a pattern to it? For instance, people from my hometown of Beckville are called Beckvillians, and people from the nearby town of Carthage are called Carthaginians (spelling?). I would guess that people from Longview are called Longviewers, though I’ve never heard the term. I know a handful of other cities across the world but that’s it. How could I decide what to call someone from Shreveport or Dallas or Tokyo? (Okay, maybe the latter isn’t applicable since it’s in a different country with another language.)
There aren’t firm rules although there are general trends. You really just have to know. People from Boston are Bostonians although they could have been Bostonites or Bostoners just as well. The city across the river has people called Cantabridgians (sp?) because people in Cambridge, England are called that.
BTW, people from Shreveport are Shreveporters. I know that because I grew up in the area.
People from Los Angeles are Angelenos, and I suppose if you want to be PC about it, Angelenas as well.
People from Rio de Janeiro are called Cariocas, and I think those from Mexico City are Chilangos. I think.
In the UK, folks from Manchester, Liverpool and Glasgow are Mancunians, Liverpudlians and Glaswegians. Blame the Romans for that.
People from Buenos Aires are Bonarenses, IIRC.
England also offers Londoners, Bristolians, Bradfordians…you do just have to know. I guess that’s also the case for English versions of foreign places (Parisians, Berliners, Muscovites…)
I’d always heard them referred to as Porteños.
I would have guessed it was similar to the case of Rio de Janeiro and Cariocas: Porteños was a popular nickname, while the more standard term was different. But according to Wikipedia, Bonaerense refers to the inhabitants of the Province of Buenos Aires, while Porteños seem to be the people of the city.
PC maybe, but certainly not gramatically correct. 
When I went to school in Cedar Hill, Texas, we joked that the town’s residents were “Cedar Hillbillies” (otherwise, they were just refered to as “Cedar Hill Residents”)
In College Station, mostly everyone can be called Aggies, though that’s mostly because of the fact that Texas A&M is in that town and has more or less dominated the local culture for a long time.
ISTR that people from Dallas were Dallasites
Also, I believe Houston has Houstonites.
Austin residents are, of course, called “Hippies”
Naughty girls from the Nutmeg State call themselves Connecticunts. The middle “c” is silent. (See diagram.)