Well of course he was, being born in the United States, in a log cabin no less! But was his father a citizen?
James Buchanan, Sr. was an Irish immigrant who arrived in the United States in 1783, between the American Revolution and the ratification of the US Constitution. James Buchanan, Jr. (the president) was born in 1791. If the father were a US Citizen, he would have to have been naturalized either in Pennsylvania before ratification of the Constitution or between March 26, 1790 (the date of the first federal naturalization act) and the birth of his son James on April 21, 1791.
The Pennsylvania Constitution, adopted September 28, 1776 provided for naturalization of aliens , meaning that Buchanan, Sr. could have been naturalized. But was he?
Every foreigner of good character who comes to settle in this state, having first taken an oath or affirmation of allegiance to the same, may purchase, or by other just means acquire, hold, and transfer land or other real estate; and after one year’s residence, shall be deemed a free denizen thereof, and entitled to all the rights of a natural born subject of this state, except that he shall not be capable of being elected a representative until after two years residence.
The names of persons who took the oath of allegiance to the state of Pennsylvania have been published. I reviewed Westcott, Thompson. Names Of Persons Who Took The Oath Of Allegiance To The State Of Pennsylvania Between The Years 1777 And 1789 : With A History Of The “Test Laws” Of Pennsylvania. Baltimore, MD, USA: Genealogical Pub. Co., 1965. (reprint). Available through Ancestry.com. No Buchanan’s whatever! (I looked at every name that started “BUC”.)
After the 1790 federal act, individuals could go before any court of record in any county, state or federal jurisdiction. They could apply in Federal District or Circuit Courts (National Archives) or before the State Supreme Court (Pennsylvania State Archives). Therefore, if an individual was not naturalized in a county court one may need to check these alternate sources. The law also allowed any court within the county to confer citizenship. After an application for citizenship was filed, there was a waiting period while the court determined the good character of the applicant.
The argument is made that under the Treaty of Paris between the United States and Great Britain (September 4, 1783 with reference to the Provisional Articles signed November 30, 1782) “colonists chose to be United States citizens and by virtue of the Treaty, Great Britain recognized those former subjects as United States citizens. This is certainly not the case. The decision in Inglis v. Trustees of Sailor’s Snug Harbor, 3 Pet. 99, 157 said: rather the treaty “ought to be co construed, as that each government should be finally deemed entitled to the allegiance of those who were at that time adhering to it.” It does not seem to me that someone arriving as the deal was being done should be considered an adherent to the United States and be excused from taking the oath required of all other foreigners. It must be said that the Americans agreed that those who were active in the Revolution before the Treaty of Peace were ipso facto citizens. But Buchanan Sr. arrived after the provisional peace accords were signed, and perhaps even after the Treaty of 1783. If someone would like to make an argument either way, I would like to see it.
I need to do more research, but the citizenship of Buchanan’s father at the time of the President’s birth is looking doubtful. Of course rather than prove a negative, the best approach would be to find out if and when he did naturalize.