The large ones, London, Paris, Tokyo, Beijing etc. have more while most smaller nation have less than a dozen. (LINK). In addition to the Marines, Embassies also have State Department Diplomatic Security officer, DoS civilian employees (LINK) and may also have civiilian contract security elements.

I think the total footprint in Iraq next year for US DoS and DoD (military training missions and military equipment delivery teams, no combat elements) and other agencies like Commerce, Agriculture and so forth (to include Contractors) is purported to be less than 6,000. Still a bunch, though Iran back in the days of the Shah had over 3,000 at times.