Some characters, such as Incidental 35 and Incidental 70, were cut from the model sheets during revisions in season 2, only to reappear in later season 13 episodes. The customer from ' Pizza Delivery,' the seventh episode made for season 1 in production order (code #107) but the third episode to be storyboarded, was the basis of Incidental 6 from ' Squeaky Boots,' the second episode made for season 1 in production order (code #102). Many of the earliest incidentals originated as storyboard drawings and became numbered incidental designs later, when multiple season 1 episodes were already storyboarded (but not yet shipped to Rough Draft Studios for animation). The following is a list of background characters, sorted by their model numbers. These model numbers usually correspond to when the characters were designed in production.

They are identified by the artists and animators with individual model numbers.

In addition to the ten main characters, SpongeBob SquarePants has over 300 background characters.