As long as the US has existed, there has been corporate personhood. The Supreme Court has argued it in terms of corporations being essentially groups of people acting together for a common cause, and noted that working together should not invalidate the rights to free speech, religious practice, entering contracts, etc. Chief Justice Marshall said it this way in 1830: "The great object of an incorporation is to bestow the character and properties of individuality on a collective and changing body of men."
Key cases (you can find them all at http://supreme.justia.com/ ):
Dartmouth College v. Woodward, 17 U.S. 518 (1819)
Providence Bank v. Billings, 29 U.S. 514 (1830)
Santa Clara County v Southern Pacific Railroad Company, 118 U.S. 394 (1886)
United States v. United Auto Workers, 352 U.S. 567 (1957)
Funny you didn't quote Marshall's much more famous saying about corporations in Dartmouth College v. Woodward:
"A corporation is an artificial being, invisible, intangible, and existing only in contemplation of law. Being the mere creature of law, it possesses only those properties which the charter of its creation confers upon it."
Key cases (you can find them all at http://supreme.justia.com/ ): Dartmouth College v. Woodward, 17 U.S. 518 (1819) Providence Bank v. Billings, 29 U.S. 514 (1830) Santa Clara County v Southern Pacific Railroad Company, 118 U.S. 394 (1886) United States v. United Auto Workers, 352 U.S. 567 (1957)
reply