This song is a remix of the City Theme from City Folk. The live performance sounds like the Night version, while the Aircheck is nearly the same as the Day version. The K.K. Slider version of the song actually made its first appearance in the Japan-exclusive CD soundtrack Animal Crossing: City Folk ~Forest Concert~ released on April 22nd, 2009. It is the 37th track on the disc and was titled City Square -K.K. Live Version-. It also was released on the CD Animal Crossing - Your Favourite Songs - Original Soundtrack in December of the same year. It is essentially the same as the live version from later games, but is slightly faster.
All of the villagers who own this song in New Horizons were introduced in City Folk.