How many professional telescopes/observatories are there in the USA and worldwide?
(Kevin): Worldwide there are about 40 telescopes larger than 2 meters (80 inches) in size at about 20 separate observatories. Considering only the USA, there are about 15 telescopes larger than 2 meters at 8 sites. The USA sites are Mauna Kea (HI), McDonald, Mt. Hopkins (AZ), Palomar (CA), Kitt Peak (AZ), Apache Point (NM), Lick (CA), and Mt. Wilson (CA). Not all telescopes on American soil are owned and/or operated by American institutions. Additionally, some telescopes on foreign soil are operated by American institutions. A complete listing from SEDS is here.