Looking on the internet deeply has found these results:

on the first floor is the most popular phrase on the web.

in the first floor 1346,000 results on the web	on the first floor 182,800,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Aug 20, 2013 ... My second apartment was located in the first floor of a building in a boatyard. It was a one bedroom, living/kitchen combo and had floor to ... I suppose I could come up with some far I noticed that the majority of new floor plans have the master suit in the first floor. The agents always brag about it like is a good feature. I want to ... Apr 3, 2015 ... The First Floor New Delhi; The First Floor, Nehru Place; Get Menu, Reviews, Contact, Location, Phone Number, Maps and more for The First ... fetched sentence involving tiles laid in the first floor while plain carpet was used in the second floor, but it's not common ...	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

in the first floor

1346,000 results on the web

on the first floor

182,800,000 results on the web

More popular!

Aug 20, 2013 ... My second apartment was located in the first floor of a building in a boatyard. It was a one bedroom, living/kitchen combo and had floor to ...
I suppose I could come up with some far
I noticed that the majority of new floor plans have the master suit in the first floor. The agents always brag about it like is a good feature. I want to ...
Apr 3, 2015 ... The First Floor New Delhi; The First Floor, Nehru Place; Get Menu, Reviews, Contact, Location, Phone Number, Maps and more for The First ...
fetched sentence involving tiles laid in the first floor while plain carpet was used in the second floor, but it's not common ...

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.