The title's pretty self explanatory! I can't seem to find a word which means exactly this, but I would be amazed if it doesn't exist.
Not quite right, but perhaps closer than other suggestions:
'Patriotism' is to 'Country' as parochialism is to 'City'.
Here are a few possibilities:
Devotion to local interests and customs.
Excessive regard for sectional or local interests; regional or local spirit, prejudice, etc.
*OT: There is a great term in Italian, campanilismo:
It would be unwise to play down the overwhelming spirit of campanilismo (local patriotism; the spirit of “our campanile is taller than yours”) during the 14th and 15th centuries.
The term refers to the bragging rights one could attain through one's town having a taller belltower than the neighboring towns. It has become a general term for pride in your hometown and its local products.
The word I think is closest to this is boosterism. It perhaps has an evangelical connotation that patriotism does not, but I think that's inherent in the difference between a city and a country. (There are significantly less onerous barriers to city residency changes than country residency changes.)
Aside from nationalism, patriotism, ethnocentrism and the dubious culturalism, the best you will likely get is the mere description of such a thing as a form of cultural bias:
Cultural bias is the phenomenon of interpreting and judging phenomena by standards inherent to one's own culture.
This term is probably way too broad to be of much use but everything else I found wasn't really technical in nature. Something more generic:
The last one is pretty close:
Fandom is a term used to refer to a subculture composed of fans characterized by a feeling of sympathy and camaraderie with others who share a common interest.
The negative side of fandom are fanboys:
Fanboy is a term used to describe a male who is highly devoted and biased in opinion towards a single subject or hobby within a given field. Fanboy-ism is often prevalent in a field of products, brands or universe of characters where very few competitors exist.
A description of a Seattle fanboy would provide the appropriate meaning. The only drawback to this is that it would likely be associated with the relevant sports team if said in a bar on a Sunday.
You can use the same form but drop the -boy for a kinder approach:
John is a NYC fan
Joan is a fan of Jersey
With, again, the entire group of fans being the fandom:
The Chicago fandom trods on