"One Mississippi, two Mississippi" is a reference to a way of counting, especially used in southern US states. Saying the word "Mississippi" after a number makes it about a second long.
Various uses of "One Mississippi, Two Mississippi, etc." include counting the seconds to estimate distance to a storm, or a children's game of hide and seek. Here, Kane Brown continually runs into a woman with whom he has an on-and-off romance. As he drowns his bourbon at the bar, Brown counts down to when there's a tap on his shoulder and they're hooking up again.
Brown wrote the song with leading Nashville songsmiths Jesse Frasure and Ernest Keith Smith, plus Alabama newcomer Levon Gray. According to Brown, the collaboration with Gray came about after Gray tagged him in an Instagram Story. Impressed with his voice and the song he'd written, Brown invited him to Music City for a co-writing session. He arrived with the title of "One Mississippi" and the meaning behind it. Brown said: "I kind of sat back and let him do his thing… He's batting 1000 for the first time we wrote."
After wowing the "What Ifs" singer and the other writers, Gray signed to Brown's Verse 2 Music publishing company.
The third verse of "Mmm Mmm Mmm Mmm" by Crash Test Dummies ("they shook and lurched all over the church floor...") was inspired by girl whose parents would speak in tongues at their Pentecostal service.