189,839 plus 125,202 in the Navy and 19,432 in the MarinesHistorically in 1939 the US army consisted of 190k men.
Note: This number counts only the Full Time (including Army Air Force) members of the National Guard (i.e., the Cadre), not the part time members who didn't start to be activated until August 1940.
Edit: It also doesn't include any volunteers like the Flying Tigers (23rd Fighter Group), Eagle Squadrons (4th Fighter Group), etc.