If I get a judgement against me for non payment, how long does it stay on my record? And how long can they still collect?

A judgement will stay on your credit report for at least 10 years. They can do wage garnishments if your state allows and attach your bank accounts until it is paid off

And to add, most places it is easy to renew the judgement from one to unlimited times, So often the judgement will stay good forever ( till you die) or till it is paid