Jonah is an interesting figure in the Old Testament, as he is a "reluctant" saint. Initially he did not want to follow God's will, but after spending three days in the belly of a whale, he changed his ways and obeyed God's command.
There is a great amount of symbolism in his story, and even Jesus Christ mentions the mythical tale of Jonah in the Gospel of Matthew:
An evil and adulterous generation seeks for a sign; but no sign shall be given to it except the sign of the prophet Jonah.
Calendars of East and West
While Jonah is not included in the universal calendar of the Roman Rite, he does have a day in the Roman Martyrology, which lists every saint that the Roman Church recognizes throughout the liturgical year.
The 2004 edition of the Roman Martyrology gives the following summary of Jonah's life on September 21:
Commemoration of Saint Jonah, prophet, son of Amittai, under whose name a book of the Old Testament is entitled; his famous exit from the belly of a large fish is interpreted in the Gospel as a prefiguration of the Lord’s Resurrection.
Many Eastern Catholics (and Eastern Orthodox) also honor Jonah on September 21, though some have his feast day on September 22, depending on which calendar they use to calculate their dates.
The Catechism of the Catholic Church affirms this tradition of honoring the lives of Old Testament saints:
The patriarchs, prophets and certain other Old Testament figures have been and always will be honored as saints in all the Church’s liturgical traditions.
If you want to read the book of Jonah, either September 21 or September 22 would be a great day to remember this fascinating Old Testament saint.