The film depicts the reconciliation of Adams and Jefferson as taking place after the death of Abigail Adams in 1818. Their famous correspondence actually started in 1812. He was well aware that she was dying before the final news came.
The film shows all troops acquitted for the Boston Massacre, however two men were found guilty of murder because they were found to fire directly into the crowd. John Adams was able to have their charges reduced to manslaughter due to a loophole in British law by proving the men could read. The two solders were punished by branding on their thumbs.
After the death of Abigail there is a scene where Dr. Benjamin Rush is consoling John Adams and encourages him to write to Thomas Jefferson. Benjamin Rush died 5 years before Abigail.
Thomas Jefferson's last words were "Is it the Fourth?" to which the reply was actually more along the lines of "Not yet, Mr. President, but it soon will be." His last words were uttered not on July 4th, but the waning hours of July 3rd. He died unconscious on the Fourth.
Despite the fact that the first two episodes span more than six years (1770-1776), neither Nabby Adams nor John Quincy Adams seem to age. Since they were born in 1765 and 1767 respectively, both should have grown and aged significantly - from toddlers to young children - over that span of time.
Episode 5 shows John Adams brushing his teeth with a toothbrush - this is not incorrect, although toothbrushing was not the most common form of dental hygiene at the time. Most people, especially the poor, would have rubbed their teeth with a rag and salt or ashes. Tooth brushes were in use in China c. 1400, in England about 1690, and mass produced tooth brushes were available in the 1780s. The modern American toothbrush was invented in 1938.
The "Join or Die" design used throughout the series preceded revolutionary ideals by more than two decades. It was designed and published in the Philadelphia Gazette in 1750 by Benjamin Franklin and was used in promoting the Albany Plan to form a united colonial government under British rule to counter the French. The plan was rejected in both Great Britain and the colonies. However, the cartoon was once again used during the Revolutionary War as a way of courting colonial unity against the British.
When John Adams (Paul Giamatti) fires two of his cabinet members, as they leave the room through the door you can see the area where the light switch has been removed and painted over.
When President John Quincy Adams is discussing his goals with his father, he states that he'll outline these objectives in his State of the Union address. The term "State of the Union Address" was not in use until 1934. At that time, 1825, it was referred to as the Annual Message to Congress.
In at least two episodes the word "escalate" is used. This word was not coined until the early 20th Century, and did not see common usage until the 1960s.
When Adams arrives in Philadelphia for the first congress, The Pennsylvania State House is shown behind him with its current steeple. In 1774 the original steeple was still in place - it had no clock.
In the series' historical era, barrel hoops were made of bent wood or of blacksmith-wrought strap iron. However, most casks and barrels pictured in the series have perfectly smooth factory-stamped strap-iron hoops (of the type made from the later 19th Century to the present).
A camera is reflected in the carriage window glass during a close-up of young John Quincy Adams just before his departure for Russia. Even the lettering (reversed in the reflection but readable) of the camera's make and model are clearly visible: ARRIFLEX 35.
General Knox is shown passing the Adams farmstead with the captured guns from Fort Ticonderoga. Braintree is 10 miles south and a bit east of their emplacement on Dorchester Heights overseeing Boston - -a considerable detour for vital ordinance.
In the scene when the army is bringing cannons past the Adams home in what was then Braintree. The direction they are moving is south away from Boston.
John Trumbull asserts that his painting, "Declaration of Independence" was well researched for authenticity, but contained many inaccuracies; principally that it showed a noticeably higher Congressional attendance than actually occurred at any given session. Even if one can grant artistic license to allow for the depiction members who were not actually present on 28 June 1776, it shows Charles Caroll of Carlton who was not only elsewhere at the time, but was not even a member yet. Caroll was elected by Maryland on 4 July and did not arrive in Philadelphia until well after that.
When John Adams is shown John Trumbull's painting, "Declaration of Independence" by Trumbull and John Quincy Adams, he comments in an archetypal scene of an elderly man looking at a group painting from long ago, that all of the men (apart from Jefferson and himself) are dead. In fact, Charles Carroll of Carrollton is the shown as the center of the three men seated in the back row, in front of the room's left door; Carroll was also alive when Adams saw the painting and he survived Adams and Jefferson by more than six years. However, Adams and Jefferson *were* the only men alive at that point who were members of the Continental Congress on 28 June 1776 when the painting takes place, and/or who voted in favor of the Declaration on 4 July 1776. Carroll was elected to office on 4 July.