Yes, and that's correct. Three battalions per regiment, three regiments per division, three divisions. That would total 27, except 3rd MarDiv has only two regiments rather than three, giving a total of 24 active-duty infantry battalions. 9th Marines were deactivated in the early '90's, and essentially replaced by three LAV battalions.
That count of 24 omits reconnaissance battalions, which some might count as infantry as well, artillery, engineers, LAV's, anti-tank, etc. And all the reservists. Btw, all of this is extremely public information.