Looking on the internet deeply has found these results:

at the city hall is the most popular phrase on the web.

at city hall 15,830,000 results on the web	at the city hall 116,400,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
There was an interested party at city hall. I got a guy who works at city hall. The department would like to set up something for you at city hall. Last time was you and me at city hall. Deputy's over at city hall right now. He's doing well at city hall. Or make your friends at city hall happy... Alderman Richard Ford was in his second term at city hall.	I'll have to be at the City Hall. Of course, that's not a problem for you there, at the City Hall. This is the security camera at the City Hall car park. Well, if even at the City Hall... Well, if even at the City Hall... We need an ambulance at the City Hall Station. (German National Anthem) Unity and Justice and Liberty... (German National Anthem) Unity and Justice and Liberty... Mother slept through a classical concert at the City Hall of Schafeberg. And the start of a gigantic and unique waste collection. We had a concert at the City Hall.

at city hall

15,830,000 results on the web

at the city hall

116,400,000 results on the web

More popular!

I'll have to be at the City Hall.
Of course, that's not a problem for you there, at the City Hall.
This is the security camera at the City Hall car park.
Well, if even at the City Hall...
Well, if even at the City Hall...
We need an ambulance at the City Hall Station.
(German National Anthem) Unity and Justice and Liberty... (German National Anthem) Unity and Justice and Liberty... Mother slept through a classical concert at the City Hall of Schafeberg. And the start of a gigantic and unique waste collection.
We had a concert at the City Hall.