McWilliams sent out on loan by Cobblers
The 18-year-old defender, the younger brother of Shaun, recently made the bench for Town's trip to Carlisle United and also played in a reserve team friendly against Cambridge United.
He's only just returned from injury and will now spend a month with St Ives, who are currently 19th in Southern League Premier Central.
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Hide Ad"Cam has just returned from injury and regular first team football will benefit his development," said manager Keith Curle.
"He will still train with us but this will give him first-team football against experienced players to learn in and develop."
McWilliams follows in the footsteps of fellow teenagers Morgan Roberts and Ryan Hughes, who are currently on a month's loan at AFC Rushden & Diamonds.
Curle added: "Morgan Roberts and Ryan Hughes are feeling the benefit of their loan spells and we hope the same happens for Cam.
"We wish him well and we will monitor his progress closely."