You cannot be put in jail for not paying a judgment. If you literally have no income or significant assets it is unlikely that a creditor will take any action against you, although he or she might do so in the future when your financial situation improves. The biggest impact of a judgment against you may be its negative impact on your credit rating.
Please note that I am only licensed in Virginia and Washington, DC. Each situation is different and I do not know all the facts about your situation. Consequently, I cannot give you specific legal advice. This communication does not create an attorney-client relationship.
Keep in mind that a judgment is valid for 20 years. Also note that if you were to go through a bankruptcy, the judgment would most likely be discharged.
If you feel like you don't owe this creditor the money they are seeking, then consult a litigation attorney and fight it.
As Atty. Hutchins mentioned, your first issue is whether you have any defense to the claim and are going to fight it. Prior to the case being heard, you will have an opportunity to speak to the creditor's attorney, who is likely representing a number of creditors and will have relatively little time to talk. The first question you might be asked is how then do you support yourself? If there is any source of income, the attorney for the creditor will want a payment plan. Be careful not to get into a plan that leads to negative amortization - you keep paying and the debt keeps going up because the payments are outweighed by interest - try to cut a deal solely for the principal amount due with interest cut off. If no payment plan and a judgment is entered against you, the attorney for the creditor, if he or she doesn't believe your income and asset claims, may start a second proceeding called supplementary process, to have you make those claims under oath, then the judge will employ a payment plan. Theoretically, the creditor can have a sheriff come after personal assets, but no one goes to the trouble or the expense of that, unless there was truly an asset of significant value. The last scenario is that the attorney believes you, realizes he/she can't get blood from a stone and drops the case - unlikely, but possible. Unlikely because, as has been said, a judgment is good for 20 years and so they can always get the judgment and wait for better times for you. Jail isn't going to happen. Bankruptcy is something to consider, but it has long term credit rating consequences just like the debt does.