Your button is definitely a Reproduction, made for civil war battle re-enactors. The Waterbury Button Company (located in Waterbury CT) changed its name to Waterbury Companies during World War 2, and that part of its backmark became Co's (short for Companies). There weren't many civil war re-enactors prior to the 1961-65 Civil War Centennial, so your button most likely was made during that time or later.