According to the National Conference of State Legislatures, accessing censored websites through alternate means becomes a legal issue in some states when done in an educational or public facility. The Child's Internet Protection Act is a federal law that provides funding for censoring software, subversion of which is illegal.
Internet censorship is largely uncommon in the United States, but filtering is employed at educational institutions such as schools and libraries to protect children from online content that is considered harmful. As of 2015, there are 24 states that have their own state laws requiring some form of protection against such content where minors have access to the Internet, NCSL notes. Some of these states merely require procedural protection such as supervision, while others require the installation of software that specifically blocks access to certain websites. All 24 states and their specific legislation are listed on the NCSL website.
The federal Child's Internet Protection Act funds and requires a certain level of Internet filtering used in schools and public libraries across the United States. According to NCSL, CIPA first went into effect in 2000 and was upheld by the Supreme Court as constitutional in 2003. The filtering software provided for by CIPA is not considered a violation of the First Amendment, because adult users may have the filtering temporarily disabled for them upon request.