Fiona entered the American consciousness with the opening of the 1954 Broadway musical Brigadoon, but didn't come onto the U.S. popularity list until 1990, and it's only in the last two years that it's entered the Top 300.
Fiona is the best known of a group of related Gaelic names, which is ironic because it's the only one without genuine traditional roots--it was found first in James Macpherson's Ossianic poems and then popularized in the late nineteenth century as a feminine pseudonym for a Scottish male writer. Its recent spike in popularity owes much to singer Fiona Apple and also possibly to Princess Fiona in Shrek.
In fact, there have been numerous Fionas on the big and small screens, from The Thorn Birds to Josie and the Pussycats, Four Weddings and a Funeral to Nurse Jackie to Shameless.
Jennie Garth and Chad Lowe have daughters named Fiona. It's also Julia Roberts' middle name.
If you're looking for something more authentic, consider Fionnuala.