Second level domains. There are waayyyyy more subdomains, as you note. You can see some information and estimates on this here: https://18f.gsa.gov/2017/01/04/

Second level domains. There are waayyyyy more subdomains, as you note. You can see some information and estimates on this here: https://18f.gsa.gov/2017/01/04/tracking-the-us-governments-progress-on-moving-https/ https://18f.gsa.gov/2017/01/04/tracking-the-us-governments-p... We (18F, me) personally measured at least 26,000 (though some of these are used as redirects or are just error pages, etc.).