Alan Shephard, Jr., one of the original Mercury 7 astronauts, was the first American in space in May of 1961, just three weeks after Yuri Gagarin of the Soviet Union although, unlike Gagarin, Shephard did not orbit the earth.
That honor, as an American, would go to John Glenn on February 20, 1962.
The original 7 included Shephard, Scott Carpenter, Gordo Cooper, John Glenn, Gus Grissom, Wally Schirra, and Deke Slayton.
Future historians will note this period as a turning point in human history.
Project Mercury had 3 primary objectives:
To orbit a manned spacecraft around Earth
To investigate man's ability to function in space
To recover both man and spacecraft safely