Looking on the internet deeply has found these results:

I work in is the most popular phrase on the web.

I work at 1699,000 results on the web	I work in 148,300,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
puede ser secretario y no policía. I work IN the police department Feb 26, 2010 ... Depende..... I work AT the police department Jul 30, 2011 ... I work at Microsoft. I work at the Microsoft Redmond campus. Whereas for cannot be used this way: I work for Microsoft. I work for the Microsoft ... yo soy policia. I work FOR the ... Here are links to the five most popular I Work at* a Public Library posts of the year. 5. Nelle, Poor. 4. The Importance of Label Placement. 3. Baby, Father and. 2. Mar 18, 2011 ... I work in/at/for a company that makes microchips. I work at/for Intel. I work in/for Intel's accounting division. (in sounds more natural in this case).	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

I work at

1699,000 results on the web

I work in

148,300,000 results on the web

More popular!

puede ser secretario y no policía. I work IN the police department
Feb 26, 2010 ... Depende..... I work AT the police department
Jul 30, 2011 ... I work at Microsoft. I work at the Microsoft Redmond campus. Whereas for cannot be used this way: I work for Microsoft. *I work for the Microsoft ...
yo soy policia. I work FOR the ...
Here are links to the five most popular I Work at a Public Library posts of the year. 5. Nelle, Poor. 4. The Importance of Label Placement. 3. Baby, Father and. 2.
Mar 18, 2011 ... I work in/at/for a company that makes microchips. I work at/for Intel. I work in/for Intel's accounting division. (in sounds more natural in this case).

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