Here's why we can assume this:
* Author Jeff Kinney: The author, Jeff Kinney, grew up in Maryland. He has mentioned in interviews that the series is inspired by his own childhood experiences.
* Setting Details: The books and movies depict a typical suburban American setting. Maryland is a state with many such suburbs.
* Visual Cues: The films feature locations that resemble the landscape and architecture of Maryland.
While the exact town or city is never confirmed, the strong connection to Maryland makes it the most likely setting for the "Diary of a Wimpy Kid" stories.