I believe he joined the LDS Church as a young adult, so no, he was not born a Mormon.
Harry Reid was born on December 2, 1939.
Harry Reid - publisher - was born in 1947.
Harry Fielding Reid was born on 1859-05-18.
Harry Reid was born on December 2, 1939.
Harry Reid was born on December 2, 1939.
Darrel Reid was born in 1957.
Miles Reid was born on January 30, 1948.
Jamie Reid was born in 1947.
Sally Reid was born in 1982.
Edward Reid was born in 1871.
Christina Reid was born in 1942.
Gavin Reid was born in 1934.