Songfacts®:

• "1 Mississippi, 2 Missisippi, 3 Missisippi" is a practice of counting as close to a second as possible. Because the word "Mississippi" is so long, it takes up enough time to make each number count equal to the passing of one second of time. The method is traditionally used by children when playing games like hide-and-seek to ensure an honest count.
• This song finds Brett Young recalling how he fell fast for a girl as he listened to her "life story on the hood of a '64 Cadillac." He used the "1-2-3-Mississippi" count to keep himself himself calm.
  
  One, I'ma lean in to kiss you
  Two, say a little too much too soon
  Three, try not to forget to breath
  I need a 1-2-3, Mississippi
  
  Young told Billboard: "I think every little boy remembers counting alligators or Mississippis when they grew up playing sports, and so I think the spin on it that we put, where it's not sports, but it's a girl - it's the mechanism that the guy has learned to kind of calm or slow himself down - I think is a cute little trick."