Their building is called The Shelley according to viewer Kipp Teague whose discerned that from the awning on the building.
However, that building is actually located in Los Angeles, the building at the real address in NYC is much different.
This is a show about nothing; however, for a show about nothing, this show has many complex plots, sub-plots, is very well written and put together.
So much so that until the public caught onto the series, the television critics were responsible for helping to keep it alive.
Viewer Jason Dean Vaupel notes that in a couple of episodes of the second season, Jerry lives in apartment 3A.