Romney was born Willard Mitt Romney on March 12, 1947 in Detroit, Michigan.
He was the youngest child of George Wilcken Romney who was thus born in Colonia Dublán, Galeana, in the Mexican state of Chihuahua – one of the Mormon colonies in Mexico – on July 8, 1907, to American parents
&
Lenore LaFount Romney who was born in Logan, Utah to Harold Arundel LaFount (1880-1952) and Alma Luella Robison (1882-1938)
If it has been established that George Romney was a citizen of the United States at the time of Mitt Romney’s birth and the remainder of the information you’ve supplied is accurate, then Mitt Romney is without doubt a natural born citizen and eligible to the Presidency.
If it hasn’t been established, it will need to be established and Romney’s eligibility should be regarded as doubtful until that time.
If it is not true that he was a citizen at the time of Mitt Romney’s birth, then Mitt Romney’s eligibility to the Presidency is, at best, in doubt. Resolution of that doubt likely would hinge upon the realities of citizenship at birth in both Mexico and the United States, as you’ve noted.
At worst, he is ineligible.
I don’t care for Romney at all as a potential candidate. But, I’m not going to try and depict an ineligibility where there is none. I won’t depict eligibility where there is none as well. Piyush Amrit “Bobby” Jindal is quite clearly not eligible. John McCain’s eligibility was and still is in doubt.
Funny how we’re suddenly surrounded with so many Presidential candidates with eligiblity issues, isn’t it? It’s almost as if somebody wants the Presidency hamstrung with foreign entanglements.