According to the best book on time-dating buttons by their backmark ("American Military Button Makers And Dealers; Their Backmarks & Dates"), your goldplated brass 2-piece button with backmark saying "Waterville" was made by the Waterville Manufacturing Company between 1847 and sometime in the 1850s, when the company went out of business. The fancy geometric design (Somewhat resembling a Sand Dollar seashell) on your button's front means it is a civilian-usage "Fashion" button, not Military.
Edit-note: I see that Nhbenz and I were typing at the same time. I'm just longer-winded than he is. ;-)