Looking on the internet deeply has found these results:

I am in office is the most popular phrase on the web.

I am at office 1124,000 results on the web	I am in office 11,770,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I got the poster boards at office plus. You said to meet at office hours. The newly constituted Supervisory Committee of OLAF took office as from December 2005 and this Report which I am pleased to submit covers our first 18 months in office. I'm no better at office friendships than you are. However, the courts have ruled that there's a limited expectation of privacy at office parties, so we... Please tell cia... File is locked in steel safe at office With guard night and day. Adam here even took a couple of early runs at office, But couldn't get elected as a dogcatcher. So meetings and managers are two major problems in businesses today, especially at offices.	in As long as I am in this office, the welfare of this fleet is not something you need to worry about. in That is why I am working extremely hard to get it on the table to propose to you while I am still in office. It is my intention to pursue that in the period of time I am in office, and to do so quickly. I am sure the President That is right and I am glad the President Office also sees it that way.

I am at office

1124,000 results on the web

I am in office

11,770,000 results on the web

More popular!

I got the poster boards at office plus.
You said to meet at office hours.
The newly constituted Supervisory Committee of OLAF took office as from December 2005 and this Report which I am pleased to submit covers our first 18 months in office.
I'm no better at office friendships than you are.
However, the courts have ruled that there's a limited expectation of privacy at office parties, so we...
Please tell cia... File is locked in steel safe at office With guard night and day.
Adam here even took a couple of early runs at office, But couldn't get elected as a dogcatcher.
So meetings and managers are two major problems in businesses today, especially at offices.

in
As long as I am in this office, the welfare of this fleet is not something you need to worry about.
in
That is why I am working extremely hard to get it on the table to propose to you while I am still in office.
It is my intention to pursue that in the period of time I am in office, and to do so quickly.
I am sure the President
That is right and I am glad the President
Office also sees it that way.