I am wondering if anyone knows what the statue of limitations is in Missouri state to file a wrongful termination suit?

This will sound sarcastic, but it's not meant to be. The limitation should be yours, not the legal systems. Most people who think they have a wrongful termination suit don't. Most people.

On the other hand, most employers don't really understand what "at-will employee" really means, either. They think it means "I can fire them for any thing or for nothing"... and it doesn't exactly mean that. But, that's another debate and not what you asked.

My only point here is that you only have one life. Be certain you want to waste ANY of it pursuing things like this. It needs to be clearly and absolutely offensive to invest your precious life into the pursuit.

In many cases, you don't have the standing you think you do, most people don't, and TIME IS MONEY, so failing your pursuit represents not only a failure to get money from your old employer, it represents a failure to GET MONEY from the time itself, too. Your time can be spent garnering meaningful compensation on your next "activities"...

Six months after leaving a job, quitting or being fired, 70% of employees find themselves in an equal and frequently better position, so it's worthwhile to move on. Looking back can be expensive, be SURE you want to invest that life blood.
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Having said that:

Meanwhile, lots of reading on Missouri law regarding wrongful termination. In a nutshell, there is no "law" regarding it directly, only specific basis for pursuing the cause at all.

TimsLaw.com » Wrongful Termination - Generally - Tim's Missouri Employment Law Info Site