There have been 12 popes named Pius so you need to be a bit more specific.
Pope Pius I was born in 0##.
Pope Pius X was born on June 2, 1835.
Pope Pius VI was born on December 27, 1717.
Pope Pius V was born on January 17, 1504.
Pope Pius II was born on October 18, 1405.
Pope Pius VIII was born on November 20, 1761.
Pope Pius XII was born on March 2, 1876.
Pope Pius IV was born on March 31, 1499.
Pope Pius XI was born on May 31, 1857.
Pope Pius VII was born on August 14, 1740.
Pope Pius III was born on 1439-05-29.
Pope Pius IX was born on 1792-05-13.