- January 1, 1990 (The 1st panel in this strip is used on the page for January 1 of the Dayspring Peanuts: A Year's Worth of Smiles and Blessings Desk Calendar)
- January 2, 1990
- January 3, 1990
- January 4, 1990
- January 5, 1990 (Lydia's name is established)
- January 6, 1990
- January 7, 1990
- January 8, 1990
- January 9, 1990 (This strip is adapted in The Peanuts Movie)
- January 10, 1990
- January 11, 1990
- January 12, 1990
- January 13, 1990
- January 14, 1990 (This strip is adapted in the episode "Too Cold" from the 2014 French TV series Peanuts)
- January 15, 1990
- January 16, 1990
- January 17, 1990
- January 18, 1990
- January 19, 1990
- January 20, 1990
- January 21, 1990
- January 22, 1990
- January 23, 1990 (This strip and the following three strips are adapted in A Charlie Brown Valentine)
- January 24, 1990
- January 25, 1990
- January 26, 1990
- January 27, 1990 (This strip is adapted in the book Friends Forever, Snoopy!)
- January 28, 1990
- January 29, 1990
- January 30, 1990
- January 31, 1990 (This strip is adapted in the episode "School Tomorrow" from the 2014 French TV series Peanuts)
| ← December 1989 | February 1990 → |