Diary

Greg's diary is his biggest job in the series. Without it, there would be no way to to know what happens in his life. So far, there have been 12 of them. The first one is red, second is dark blue, 3rd is dark green, 4th is yellow, 5th is purple, 6th is icy blue, 7 is brown, 8 is lime green, 9 is orange, 10 is black, 11 is red-orange, and 12 is blue-green. All of them say DIARY on the cover. Greg exclaims how he told Susan to get one that doesn't say the word diary, but his mother still got one that said diary, probably because it was cheaper or she didn’t hear part of it and thought Greg wanted her to get one that had the word diary on it. All of them have little drawings between the texts based on what Greg's talking about. Each Diary has 217 pages and some of them also have 17 activity pages and the activities are extracted from the Do-It Yourself Book. In all the descriptions and summaries, it has been labeled as a diary, but it is exactly Greg's journal, and that's how he got mad at his mom for buying that book until Greg saw Rowley's new diary.

Trivia

 * ​Each diary has its own months. So far in all Diaries, there are a total of 32 months which is the same as  2 years and 8-months.
 * Its owns September, October, November, December, January, February, March, April, May, and June.
 * 2nd owns September, October, November, and December.
 * 3rd owns January, February, March, April, May, and June.
 * 4th owns June, July, and August.
 * 5th owns September, October, and November.
 * The 6th,7th, 8th, and 10th book have the 2 months . 6th owns November and December and 7th  owns January and February and 8th owns March and April, 10th book owns September and October.
 * The 9th has only 1 month, June.
 * In Rodrick Rules, it was later revealed that Rodrick snatched Greg's diary and ran, but tripped over a board game. Greg quickly got the diary and went to the Leisure Tower's Women's bathroom without noticing and destroyed the first diary by flushing it in the toilet. Then when the security came and got him out, Rodrick saw the whole thing and blew his secret 4-6 months later, and the story ended up changing to infiltrating the high school cheerleading locker room.
 * Greg rips out certain pages of his diary, which can be seen in movies and games sometimes. In the first and second Diary of a Wimpy Kid movies, you see pages which were never in the book, meaning Greg probably ripped them out.
 * Considering Greg to be 11 in Diary of a Wimpy Kid (since he was in 6th grade), if the series is not timeless, Greg would be about 13 and almost 14 (by The Long Haul, since it ends in June) but since Jeff Kinney said its timeless it is very unlikely. If considered 12 then he would be 14 (almost 15).
 * Greg only aged once in the book Dog Days he is shown celebrating his 13th birthday Greg didn't age or celebrate his birthday on the summers of Rodrick Rules (which we never see it happen)and The Long Haul which would make him 13 and in the 7th Grade.
 * The Long Haul is the first time since the first book that there are missing months between the current book and previous book, May is missing.
 * Greg considered the diary as a journal.
 * Greg's diary is not mentioned in the books Dog Days up to Double Down (except for Third Wheel)
 * Greg's diary is not mentioned in the films Dog Days and The Long Haul outside of when Greg is narrating it.

Year 1

 * Diary of a Wimpy Kid (September-December)

Year 2

 * Diary of a Wimpy Kid (January-June)
 * Missing months (July and August)
 * Diary of a Wimpy Kid: Rodrick Rules (September- December)

Year 3

 * Diary of a Wimpy Kid: The Last Straw (January-June)
 * Diary of a Wimpy Kid: Dog Days (June-August)
 * Diary of a Wimpy Kid: The Ugly Truth (September-November)
 * Diary of a Wimpy Kid: Cabin Fever (November and December)

Year 4

 * Diary of a Wimpy Kid: The Third Wheel (January and February)
 * Diary of a Wimpy Kid: Hard Luck (March and April)
 * Missing month (May)
 * Diary of a Wimpy Kid: The Long Haul (June)
 * Missing month (July and August)
 * Diary of a Wimpy Kid: Old School (September and October)

Year 5
It also happens that the books were published in chronological order, considering that the order above is the same as the order each book was published.
 * Diary of a Wimpy Kid: Double Down (October and November)