This song did not have a title when it was first performed. In concert JoCo called it "Untitled Song About Marriage" and set lists had it listed as both "40" and "Upon Turning 40." Photos of two set lists from March can be viewed here and here on Flickr. The official name wasn't revealed until the album Artificial Heart was released.
This song was performed in concert for the first time on March 25th, 2011 in Asheville, NC. That performance can be viewed on YouTube.