Factual error: In one scene Lord Cornwallis' adjutant announces to Lord Cornwallis that a messenger (Benjamin Martin) has arrived. After initially dismissing the message, Lord C. pays attention on the mention of two "Great Danes" in Martin's company. The Great Dane as we know it today had many names over the centuries, but the Danish connection only became common use in the 19th century (Comte de Buffon - l'Histoire Naturelle - 1811). Until then the British would have called them Mastiffs (English or German), English Dogges, or perhaps even Boarhounds. Actually - the English Kennel Club of Britain didn't officially recognize the term/breed "Great Dane" until 1884.
Factual error: When Benjamin Martin and his family go to Charleston, the first view we see of the city is a shot from a hilltop, looking down on the city from the north. Charleston is a port city in the "Lowcountry" of South Carolina, a broad coastal plain. Thus, the land around the city is extremely flat, and the nearest hill of that elevation is at least 80 miles inland.
Factual error: Although the historical advisor for the film is The Smithsonian Institute it does not seem to have noticed that the toy soldiers used in the film (some in superb close-up} are all dressed in uniforms of the mid to late 19th cent., i.e. approx. 100 years later than when the film is set.
Factual error: In the scene at Lord Cornwallis' outdoor party celebration, right after Benjamin Martin and his Continental Army blows up a British Ship, one of Lord Cornwallis' Captains throws back a big gulp of his drink from his Martini glass in grief and disbelief - the problem is this movie takes place in the mid 1700s and the Martini Glass wasn't invented until the 1920s, during the Roaring Jazz days.
Factual error: Mel Gibson's son has toy soldiers from the future. In one shot when he is melting one of the soldiers it is visible. Although it has a red uniform it isn't a British soldier. In fact it depicts Hofburg Trabanten Leibgarde which was the personal guard of the sovereign originally from Austria, in uniform from around 1850 - 1918.