How Many People Have Walked On The Moon?

12, all between 1969 and 1972.  All American-born men and citizens.  They are listed with the year of their landing and their age at the time:

1969: Neil Armstrong (38), Buzz Aldrin (39), Pete Conrad (39), Alan Bean (37).
1971: Alan Shepard (47), Edgar Michell (40), David Scott (39), James Irwin (38).
1972: John Young (41), Charles Duke (36), Eugene Cernan (38), Harrison Schmitt (37).

A further 12 individuals also circled the moon during the same period, but did not set foot on it.

Alan Shepard also has the distinction of being the first American astronaut (man in space), having flown in the Freedom 7 aircraft in 1961 to 116 miles above the Earth.

James Irwin was the first to drive a lunar rover on the Moon.

The USSR sent at least 20 manned missions to circle the moon, and has landed unmanned probes on the Moon.  The Soviets achieved the first impact and first safe landing of probes on the moon.  But no cosmonauts ever landed there.

Twelve astronauts have walked on the moon, the last in 1972.

Here are the names of those astronauts listed chronologically by the date of their walk.

July 20, 1969: Neil Armstrong and Edwin "Buzz" Aldrin

Nov. 19, 1969: Charles (Pete) Conrad and Alan Bean

Feb. 5, 1971: Alan Shepard and Edgar Mitchell

July 30, 1971: James Irwin and David Scott

Apr. 21-23, 1972: Charles Duke and John Young

Dec. 11-13, 1972: Harrison Schmitt and Eugene Cernan

The total number of people that walked on the Moon's surface is 12.
All Apollo flights that went to the Moon carried 3 astronauts, 2 of which were to land on the Moon's surface. There were 7 Apollo flights that were supposed to go to the Moon. However, Apollo 13 had an explosion while en-route to the Moon and therefore did not land on the Moon. So a total of 12 astronauts walked on it's surface.

Twelve, all Americans. Two each from Apollos 11, 12, 14, 15, 16, 17.

12, all between 1969 and 1972.  All American-born men and citizens. 
1969: Neil Armstrong (38), Buzz Aldrin (39), Pete Conrad (39), Alan Bean (37).
1971: Alan Shepard (47), Edgar Michell (40), David Scott (39), James Irwin (38).
1972: John Young (41), Charles Duke (36), Eugene Cernan (38), Harrison Schmitt (37).

I think it's 12.

12