Your solid-cast brass 1-piece button has a "Livery" emblem, showing a coronet (not a crown) above a "Family Crest" shield. If I recall correctly, a coronet having 9 knobs signifies the aristocratic rank of Viscount.
Solid-cast brass 1-piece buttons with a "pillar" shank are still being manufactured today... so they can be extremely difficult to accurately time-date. I cannot say with any certainty whether yours is from the mid-1800s or the mid-1900s. The fact that in the photos it has very little oxidation on the brass suggests it is from recent times. If so, it might be a Fashion button, rather than an actual Livery button. You'd have to do some research looking for a match-up of that exact emblem among actual Livery buttons to see whether it is a real one or a "faux" Livery emblem used on modernday Fashion buttons.