Taylor Swift -- Buys $17 Million Mansion ... WITH CASH!!!

Taylor Swift is a certified BALLER -- TMZ has learned that not only did she just buy a Rhode Island mansion for $17 million ... but she did it with straight cash, homey!

As TMZ first reported, Swift was eyeing the 11k-plus-square-foot mansion for a few weeks now, having toured the place back on April 15.

According to our real estate sources, the asking price on the house (which sits on 5.23 acres) was around $20 mil, but Swift got it for $17.75 mil.

We're told Swift wired the money over and movers were spotted at the house early this morning.