Where is the narrator at the beginning of "The Black Cat" by Edgar Allan Poe?

The answer
to this question can be found in a very close reading of the text, and also in using inference,
or an educated guess, to figure out where he is.  At the beginning of the story, he starts out
by addressing the audience and telling them why he wants to tell his tale:

"But tomorrow I die, and today I would unburthen my
soul."

So, wherever he is, he knows that tomorrow he
is going to die, and he wants to let everyone know what happened before he does.  This implies
that he is possibly in jail, about to be executed the next day.  Either that, or he is going to
kill himself, and wants to share his story before he does that.  So, given those two
alternatives, let's look at what happens to him at the end of the story that he tells.  He is
with the cops, in his house, so confident of getting away with his crime that he hammers on the
walls to show them how sound they are.  Unfortunately for him, he hammers through the wall and
the rotting corpse of his wife falls out.  From this we can assume that he was arrested--they
had the body right in front of them, so it was pretty solid proof.

Piecing
together what happened at the end, and the fact that he says he is going to die the next day and
so much tell his story, I would guess that he is in prison, about to be executed for the crime
of murdering his wife.  His story is his last confession before he dies.  I hope that those
thoughts helped; good luck!