Kenicott v. The Supervisors was a United States Supreme Court case that was decided in 1872. The case involved a dispute between the plaintiff, William Kenicott, and the defendant, the Supervisors of the County of Rock Island, Illinois. Kenicott had been appointed as a justice of the peace in the county, but the Supervisors refused to pay him the salary that was due to him. Kenicott argued that the Supervisors had violated the Fourteenth Amendment of the United States Constitution, which states that no state shall "deny to any person within its jurisdiction the equal protection of the laws." The Supreme Court agreed with Kenicott, ruling that the Supervisors had violated the Fourteenth Amendment by denying him the salary that was due to him. The Court held that the Supervisors had acted in an arbitrary and capricious manner, and that they had violated Kenicott's right to equal protection under the law. The Court's decision in Kenicott v. The Supervisors established the principle that the Fourteenth Amendment protects individuals from arbitrary and capricious actions by state governments. This decision has been cited in numerous cases since then, and it has been used to protect individuals from discrimination and other forms of unequal treatment.

In Kenicott v. The Supervisors, the Supreme Court was asked to decide whether a tax levied by the supervisors of Rock Island County in Illinois on certain railroad property within their jurisdiction was unconstitutional. Justice Field delivered the opinion of the court and held that it was not unconstitutional because there had been no violation of any constitutional provision or principle. However, Chief Justice Chase dissented from this opinion and argued that while Congress has exclusive power over interstate commerce, states have concurrent authority to impose taxes on such commerce so long as they do not interfere with its free flow across state lines. He further argued that since this particular tax did nothing more than raise revenue for local purposes without interfering with interstate commerce, it should be upheld as valid under both federal and state law.