https://www.law.cornell.edu/uscode/text/42/1983

This one?

Every person who, under color of any statute, ordinance, regulation, custom, or usage, of any State or Territory or the District of Columbia, subjects, or causes to be subjected, any citizen of the United States or other person within the jurisdiction thereof to the deprivation of any rights, privileges, or immunities secured by the Constitution and laws, shall be liable to the party injured in an action at law, suit in equity, or other proper proceeding for redress, except that in any action brought against a judicial officer for an act or omission taken in such officer’s judicial capacity, injunctive relief shall not be granted unless a declaratory decree was violated or declaratory relief was unavailable. For the purposes of this section, any Act of Congress applicable exclusively to the District of Columbia shall be considered to be a statute of the District of Columbia.

(R.S. § 1979; Pub. L. 96–170, § 1, Dec. 29, 1979, 93 Stat. 1284; Pub. L. 104–317, title III, § 309(c), Oct. 19, 1996, 110 Stat. 3853.)

or this one?

https://www.acludc.org/en/news/happy-150th-anniversary-section-1983

On April 20, 1871, President Ulysses S. Grant signed one of the most important civil rights laws in U.S. history: the Ku Klux Klan Act. Section 1 of that law – known today as 42 U.S.C. § 1983 – empowers individuals to sue state and local government officials who violate their federal constitutional rights. The law was aimed at protecting Black Americans from white supremacist violence and murder in the postbellum South.

Section 1983 was invoked by the plaintiffs in Brown v. Board of Education (you can see the Act cited by its date) when they challenged school segregation 70 years ago. ACLU offices nationwide continue to use Section 1983 today to defend and advance the rights of all people.