Reuters asked for and obtained Mitt Romney's birth certificate:
Yes, Republican Mitt Romney appears eligible to be president, according to a copy of Romney's birth certificate released to Reuters by his campaign. Willard Mitt Romney, the certificate says, was born in Detroit on March 12, 1947.
His mother, Lenore, was born in Utah and his father, former Michigan governor and one-time Republican presidential candidate George Romney, was born in Mexico.
See the certificate here.