Early 19th century; earliest use found in Thomas Creevey (1768–1838), politician. Apparently alteration of either popelot or French populo baby, tot (1490 in Middle French; from poupelin, with expressive alteration of the ending).
Definition of poplolly in US English:
poplolly
nounˈpɒplɒli
rare
A mistress.
Origin
Early 19th century; earliest use found in Thomas Creevey (1768–1838), politician. Apparently alteration of either popelot or French populo baby, tot (1490 in Middle French; from poupelin, with expressive alteration of the ending).