In Wis. OB the word is 'illicit', not unlawful.
"Not sanctioned by custom or law; unlawful."
Premarital sex, adultery, and other ethical issues arising from sexual relations between consenting heterosexuals who have reached the age of consent have generally been viewed as matters of private morality, and so, have not generally been prosecuted as criminal offenses in the common law.[4] This legal position was inherited by the U.S. from the U.K.. Later, some jurisdictions, a total of 16 in the southern and eastern United States, as well as the states of Wisconsin[5] and Utah[6] passed statutes creating the offense of "fornication" that prohibited (vaginal) sexual intercourse between two unmarried people of the opposite sex. Most of these laws either were repealed, were not enforced, or were struck down by the courts in several states as being odious to their state constitutions. See also State v. Saunders, 381 A.2d 333 (N.J. 1977), Martin v. Ziherl, 607 S.E.2d 367 (Va. 2005).