How many infantry divisions in World War 1?

The US sent 43 infantry divisions to France in WWI, and 21 of them saw enough action to sustain one thousand men or more killed in action. Seven became "Depot Divisions" and worked in the Service of Supply, and four were broken up and their personnel used as replacements for other divisions.

The WWI US Infantry Divisions were huge, around 27,000 men in four large regiments. This was the equivalent to two or three divisions of all other combatant nations.

There were three types of US Infantry divisions. Low numbers, 1 to 9, were supposedly "regular army", but all had a large number of wartime volunteers and draftees. Numbers 26-50 were National Guard divisions from the states, called into active service ("Federalized"). There were more National Guard Divisions sent to France than any other type. Numbers 76-93 were so-called "National Army" divisions, intended to be made up of draftees, grouped according to state of origin like the National Guard Divisions. In actual fact all three types of divisions had a mixture of prewar regulars, draftees and volunteers.