Ron is eight years old when he writes that will. What shrewd fans really want to know is how that Ron Swanson becomes the filthy rich Ron who quietly oversees the Pawnee Parks Department (which certainly doesn't pay enough to explain how he purchased an entire Lagavulin distillery).
One Redditor suggests that before his time in the government, Ron may have been a criminal overlord in Pawnee. The theory considers not only Ron's fortune, but his protectiveness of his private life and how much he loathes the government (and following anyone's rules but his). He has a unique set of skills, including wilderness survival and weaponry, and is well-versed in living a double life due to his secret identity as swoon-worthy saxophonist Duke Silver.
It's unlikely that Ron came into his money through traditional means. We know he invests in gold and silver, not stocks. We've met his mother and know that it isn't family money. He's refused to do his woodworking for profit. Although he's been working nonstop from a young age, and could have amassed significant savings, none of his positions have been very lucrative. He doesn't trust banks, so he wouldn't have accrued interest.
Unless the ladies in Eagleton are paying Duke Silver incredibly handsomely, we have to assume there's another explanation for Ron Swanson's stash — and fans are getting pretty creative with their answers to this mystery. We'll just have to keep speculating about Ron's wealth.
