The song is a moderate up-tempo describing a woman meeting a man at a club and later eloping with him in Las Vegas after having had too much to drink that night.

She wakes up the next morning, "thinkin' 'bout Elvis somewhere in Vegas", to discover that she does not even know her last name (i.e., she married the man while she was still intoxicated), and worries that her "mama would be so ashamed."

"[3] Rolling Stone picked the track as their favorite, saying "the most fun is "Last Name," where she gets wasted and runs off to Vegas with a guy she doesn't know.

[8] Underwood performed the song live for the first time on television during the 43rd Annual Academy of Country Music Awards on May 18, 2008.

They make it out to Las Vegas where they participate in a couple of gambling activities such as roulette and a Wheel of Fortune game where they win a new truck.

[9] It is the third country number one from Carnival Ride and reached the top of the chart faster than the first two singles, taking only 13 weeks.