The 21-year old midfielder has joined the Swans from Liverpool and Williams feels the inclusion is more reason for fans to get excited.
"Jonjo is a quality signing for us," Williams told the club's official website. "We know what he can do as we've played against him a number of times, while he has represented England as well so that proves his quality.
"It's such an exciting time to be a Swansea fan. Everyone has enjoyed the massive success the club has tasted recently, and now we are looking forward to another exciting adventure."