Can you count the interest on a mortgage of a house you do not live in.?

Yes, it is considered your second home. As long as nobody pays rent of any kind, it is just a home. You are still have limits as to the amounts.

https://turbotax.intuit.com/tax-tips/home-ownership/deducting-mortgage-interest-faqs/L4a9KF9mI

Yes, the IRS lets you deduct your mortgage interest, on a second home, but only if you itemize deductions. You can't deduct the principal (the borrowed money you're paying back).

In addition to itemizing, these conditions must be met for mortgage interest to be deductible:

• The loan is secured, which means the lender has some kind of guarantee of payment, usually in the form of property. If a borrower defaults on payments, the lender can seize the property that’s securing the loan. If you’re buying or refinancing a home, especially if it’s your first home, the loan is usually secured by the home you’re buying or refinancing
• The home with the secured loan must have sleeping, cooking, and toilet facilities
• The debt can’t exceed $750,000 (or $1,000,000 if the loan was taken before December 16, 2017) to get the full deduction
• You or someone on your tax return must have signed or co-signed the loan.
• Click here to read the entire TurboTax FAQ.