Greg's journal is his biggest job in the Diary of a Wimpy Kid (series). Without it, there would be no way to know what happens in his life. So far, there have been 13 of them. The 1st one is red, 2nd is blue, 3rd is green, 4th is yellow, 5th is purple, 6th is cyan, 7th is brown, 8th is lime green, 9th is orange, 10th is black, 11th is red-orange, 12th is blue-green, and 13th is violet. All of them say DIARY on the cover, Not JOURNAL. Greg explains how he told Susan to get one that doesn't say the word diary, but Susan 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, though 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.
- Each diary has its own months. So far in all Diaries, there are a total of 38 months, which is the same as 3 years and 2 months.
- 1st 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.
- 6th owns November and December.
- 7th owns January and February.
- 8th owns March and April.
- 9th owns June.
- 10th owns September and October.
- 11th owns October and November.
- 12th owns December.
- 13th owns January and February.
- 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. As a result, he became very popular.
- 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 it's timeless it is very unlikely. If considered 12 then he would be 14 (almost 15).
- The Long Haul is the first time since Diary of a Wimpy Kid 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 The Getaway (except for The Third Wheel and Double Down)
- Greg’s diary is not mentioned in the Dog Days and The Long Haul films outside of when Greg is narrating it.
- Diary of a Wimpy Kid (September-December)
- Diary of a Wimpy Kid (January-June)
- Missing months (July and August)
- Diary of a Wimpy Kid: Rodrick Rules (September- December)
- 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)
- 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 months (July and August)
- Diary of a Wimpy Kid: Old School (September and October)
- Diary of a Wimpy Kid: Double Down (October and November)
- Diary of a Wimpy Kid: The Getaway (December)
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.