I live and work in the state of Illinois since April 2006 and pay rent for an apartment.

I own an apartment in Puerto Rico that use as my primary residence
There. I have a mortgage on this property and would like to know if
I can ideduct the interest expense when I file my US tax return. Puerto Rico
Is an associated state and a commonwealth of the US.

Thank you

Yes, you can claim mortgage interest deductions if you itemize your deductions.