No one will really know for sure, since audio of the event wasn't recorded. That technology was another two score years away in the future.
But there are at least nine versions of the Gettysburg Address from the time period, with some in Lincoln's handwriting. All are slightly different, and not all accounts agree that Lincoln mentioned God during the 270-word, two-minute speech.
Lincoln was invited as guest speaker at the Gettysburg cemetery event as a courtesy, and it wasn't entirely expected he would attend. The famed orator Edward Everett was the featured speaker.
Lincoln and his staff arrived on the day before the event, and Lincoln compared notes with Everett. The president also worked on his speech that night.
Only one picture of Lincoln at the Gettysburg ceremony exists, taken well before his speech. Everett spoke first, for about two hours, in the tradition of the day.
Lincoln was described as looking pale as he rose at the end of the ceremony to speak.
Accounts from the time period said he was applauded, then left to go back to Washington.
Historians are still debating where the event took place on the Gettysburg battlefield.
The Gettysburg Address itself is not in question. The Associated Press and three newspapers transcribed the remarks for publication. Lincoln gave his draft copy and a copy written right after the speech to his secretaries.
In later days, Lincoln wrote out three other copies as mementos, giving us a total of nine versions of the speech. All nine are different.
The gist of all the versions is the same, and all the versions contain the quotes widely taught in history class.
However, the first two versions, in Lincoln's own handwriting, omit the mention of God in the conclusion.
"The nation, shall have a new birth of freedom, and that government of the people by the people for the people, shall not perish from the earth," Lincoln wrote in his first two versions. Later versions added the word "under God" so that the sentence reads, "the nation, under God, shall …"
The inclusion of God in the speech is perhaps the most significant difference among the versions. The fifth version of the speech, which was signed and dated by Lincoln, was considered the "final" version and included "under God" in its last sentence.
But is that what Lincoln actually said on the battlefield?
In "The Collected Works Of Abraham Lincoln: Volume 7," the dispute seems to be settled.
The Associated Press report of the speech, written by Joseph Gilbert, along with reports from newspapers in Philadelphia and Chicago, all agree that Lincoln said "under God" as his speech concluded.
In that book's footnotes, it's explained that the Philadelphia Inquirer and Chicago Tribune had the words in its independent accounts.
"These papers corroborate Gilbert's version, however, in having the phrase 'under God,' which Lincoln must have used for the first time as he spoke," the book says.
It also appears that Lincoln used the Associated Press version as a reference point when he wrote out the third, fourth, and fifth versions.
A fourth printed version, from the Boston Advertiser, shows that Lincoln used the words "under God" as the address concluded.
In an interesting historical twist, Lincoln's fourth version of the address, called the Bancroft copy, was rejected by a book publisher who wanted it in 1864.
George Bancroft was a historian who asked Lincoln to write down a version for a compilation, but Lincoln wrote on both sides of the paper, which made it unusable.
In March 1864, Lincoln's office received a letter from an official named John Kennedy to explain that the Bancroft copy wouldn't fit into the proposed volume.
Scott Bomboy is the editor-in-chief of the National Constitution Center.