Were US soldiers in World War 1 mobilized in units by states or was the draftee population all thrown together?

Answer 1

Both.

The Army system of divisions today goes back to 1917. Before this time the US Army had divisions only when there was a war going on. For WWI the Army needed to create a much larger force than had ever been seen in US history. The divisions the US created for WWI were much larger than those of any other nation - about 26,000 men. Forty three of these divisions were sent to France before the war ended.

The system the army developed was that low numbers, 1 to 25, were for "regular army" divisions. There were nowhere near enough peacetime prewar professional soldiers to make this many divisions. Eventually the 1st through the 8th Divisions got to France, and they had prewar regulars, enlistees and draftees on the roster. One half of the US 2nd Division was US Marines in the Marine Brigade. The other half was army doughboys. The origin of the personnel was "at large", meaning from anywhere. Only the 1st through the 5th saw extensive action, and the 8th got to France just before the Armistice.

Division numbers 26-50 were reserved for National Guard Divisions. (And still are, but I believe its numbers 26-70 now). This was the National Guard of each state called into active service. Even before shipping out they were filled out with enlistees and draftees without regard to geographic origin, but they retained a lot of local flavor. After they got into action replacements came from anywhere. There were actually more National Guard troops to see action in France than any other type. The 26th through the 42nd Divisions got to France, but the personnel of the 34th and 38th Divisions were used as replacements for other divisions, and the 31st, 39th and 40th Divisions became "Depot Divisions" in the Service of Supply. The 41st Division saw a little action then it too became a Depot Division. The 42nd Divisions nickname was "The Rainbow Division" because the units which were in it were from several different states. So in all eleven National Guard Divisions saw extensive action, and some were among the best in the AEF.

Numbers 51 and up were to be so-called "National Army" divisions, made up of draftees, and grouped into divisions from specific states, like the National Guard Divisions. There would of course be a cadre of professionals as the backbone of such divisions. In practice both enlistees and draftees served in these divisions. Two of these high-number divisions, the 92nd and 93rd, were made up of black soldiers. One was used as labor troops and the other fought with the French. Some units making up the one which fought with the French were black National Guard units. So it was not an inflexible, iron-clad system. The 76th through the 93rd "National Army" divisions got to France before the Armistice. The personnel of the 84th and 86th divisions were used as replacements for other divisions, and the 76th, 83rd and 85th Divisions became Depot Divisions. The 82nd Division (which became Airborne on the eve of WWII) was the "All American" because, like the 42nd, its personnel were from all over. Nine "National Army" Divisions saw a lot of action.