The painting is as close to a documentary material source as was possible in the pre-photography era. It was created between 1817 and 1819, at that time Trumbull was able to paint many of figures from life, he also visited the Pennsylvania State House and depicted the actual chamber where the Second Continental Congress met. However, as a lot of painters before him, he took a liberty to modify the reality to express his vision - the painting depicts 42 of 56 signers but has some characters that did not sign. There is even a belief that as a way to sign the picture Trumbull painted himself as one of the additional characters.
Despite the picture name given by Trumbull, 'The Declaration of Independence, July 4, 1776', the date the painting depicts is not actually the 4th of July, it is June 28th, when a draft of the Declaration of Independence was presented to John Hancock, the president of the Continental Congress. The five members that presented the draft of the Declaration are John Adams, Roger Sherman, Robert Livingston, Thomas Jefferson and Benjamin Franklin.
There is a funny belief associated with the painting - it looks like Thomas Jefferson is portrayed stepping on John Adams’ foot, an action symbolizing the pair as political enemies. Here is an enlarged part of the painting and I’ll let you be the judge.