Let’s Encrypt is a free open Certificate Authority.
https://letsencrypt.org
SSL Certificates · Root Authority
Get access to data on 43,791,073 websites that are LetsEncrypt Customers. We know of 2,000,001 live websites using LetsEncrypt and an additional 41,791,072 sites that used LetsEncrypt historically and 1,079,759 websites in the United States.
We know of at least 43,791,073 live websites using LetsEncrypt.