HiCustomer I would unplug everything that is plugged in to the outlets on that circuit, then check the breaker again to see if it will hold. It could also be a blown light bulb that is causing the short. This is very rare, but I have seen it a couple of times in my career.

The breaker itself may have failed. You can check for this by removing the Panel cover, loosening the screw on that breaker, and removing the wire from the breaker. Once the wire is disconnected from the breaker, turn the breaker on to see if it will hold. If it does, the breaker is not the problem.

If you rule out the breaker, your next step should be opening Outlet boxes and light Switch boxes to look for a short. A short is when the Hot Wire touches the neutral or bare ground wire. Look for arc marks on the bare ground wires, and on the screws on the sides of the outlets and switches.

If you see arc marks, you can wrap the bare wire with tape and make sure it gets pushed all the way to the back of the box when you reinstall that particular device. Make sure all connections are tight in any boxes you open, including your electrical panel. If you are uncomfortable working around live electricity, you should leave it to a professional electrician.

If you find any outlets or switches connected via the small push-in holes on the back, I strongly recommend redoing the connections using the side screws.