Idaho Gov. Little signed HB 421, defining sex and gender as binary biological categories across state code

On April 9, 2024, Idaho Governor Brad Little signed House Bill 421, which inserts binary, biology-based definitions of "sex," "male," "female," and related terms into Idaho Code section 73-114 — the general statutory-terms section that applies by default across all Idaho statutes unless a specific law defines a term otherwise. The law declares there are "two, and only two, sexes," provides that an individual's sex is determined at conception or birth and never by self-identification, and defines "gender" as a synonym for biological sex, explicitly excluding gender identity, expression, or role.

Because section 73-114 supplies default definitions for the entire code, the measure writes gender identity out of the legal meaning of "sex" and "gender" statewide. The bill also amends specific statutes to point to the new definition, including Idaho Code section 39-245A governing the sex recorded on birth certificates, the Vulnerable Child Protection Act (section 18-1506C), and the public-school changing-facility statutes (sections 33-6602 and 33-6702). The bill's sponsor, Sen. Ben Adams, R-Nampa, said gender is referenced dozens of times in Idaho law and always references biological sex, arguing the measure "is fundamentally defining what we already know."

House Bill 421 passed the Idaho House 54-14 and the Senate 26-8. Governor Little signed it as Session Law Chapter 322, and its emergency clause set an effective date of July 1, 2024. The definitional framework it established is subsequently invoked by later Idaho statutes, including the state's 2025 measures restricting transgender residents' access to public facilities.