A contractor from another county in the state of Missouri has reneged on his contract. Do I have to file suit in his county?

That sounds like a very frustrating situation.  Generally speaking, you could probably sue the contractor in your county rather than his county, but there are facts that could change the answer. For example, some contracts require that suit be filed in a particular county. Your question doesn't state whether you have a written contract with the contractor or, if you do, whether the contract limits where a lawsuit can be filed.  It is also not clear whether your contract defines when the work must be completed. The proper county for filing suit can vary depending upon the claims in the lawsuit and other facts that are not included in your question.  Finally, there may be reasons that you would want to file suit in the contractor's county. Some counties may be better suited for your lawsuit than others. The best course of action is to find a local lawyer who can advise you about your specific situation. Your lawyer can advise you where you can file suit and also where you should file suit.  Best regards.