Bouvier's Law Dictionary, Revised 6th Ed (1856):

INCEST. The carnal copulation of a man and a woman related to each other in
any of the degrees within which marriage is prohibited by law. Vide
Marriage. It is punished by fine and imprisonment, under the laws of the
respective states., Vide 1 Smith's Laws of Pennsylv. 26; Dane's Ab. Index,
h.t.; Dig. 23, 2, 68; 6 Conn. R. 446; Penal Laws of China, B. 1, s. 2, Sec.
10; Sw. part 2 Sec. 17, p. 103.