Kilkenny has agreed a two-year deal for an undisclosed fee, having played 15 times for Bournemouth after spending time on loan at Fleetwood Town last season.
He spoke about the move and how he needed to be at a club that wanted him.
"I needed a new home and now I feel like it's time for me to make this place a permanent home for me," the former Republic of Ireland U21 international said.
"I like to get on the ball and get the team playing and I feel like I can bring that to the team."
Butterworth has seven goals and three assists in 59 appearances in League One during the past two seasons after joining from Port Vale in 2022.
Both of these talents will be hoping to make a major impact at Swindon this season as they look to escape League Two.