Tim Berners-Lee published “a short summary of the
 WorldWideWeb project” on the newsgroup alt.hypertext Aug. 6, 1991.

Mike Murphy at Quartz has more:

The first website, which was literally a website explaining what a website was, went online in November 1992. It was created by Tim Berners-Lee, at the time a researcher at CERN (the European Organization for Nuclear Research). But before the site went live, Berners-Lee brought up the project he was working on — hyperlinks, the technology that allows pieces of information to be linked to each other on the internet — on a Usenet page. Usenet was a pre-internet forum when just a couple million people were on the internet; its archives have since been acquired by Google. If you want to find the first rumblings of the modern web online now, you have to trudge through some incompletely archived pages on Google Groups.

Berners-Lee was responding to a question someone asked about whether anyone knew anyone working on the concept of hyperlinks. As one of the people directly working on that exact topic he seemed perfectly situated to respond.