Plantin wrote a great many letters, mostly in French or Latin. Toward the end of his life, too sick and weak to write, he dictated his letters to his partner and son-in-law Jan Moretus. Much of Plantin's correspondence is preserved in the archives of the Plantin-Moretus Museum in Antwerp.

Two letters to Consalus Ponce de Leon are available, written in 1888 and 1889, in Latin; the 1889 letter was written by Moretus after Plantin's death. The tone of these letters suggests that Plantin and Ponce de Leon were friends, not just publisher and author. (The numbers 1395, 1398 and 1481 are the identifiers in Correspondance de Christophe Plantin. The text in brackets following each letter is a paraphrase rather than an exact translation of the Latin or French.)

1395. - Plantin to Ponce de Leon.
(Archives Plantiniennes, X, fo 238v).
22 August 1588.

Rev. admodum doctissimoque D. Ponce a Leon,
Smi D. Nostri Papæ; cubiculario secreto S. P.

Tuas X Kal. Junii scriptas accepi ex quibus intelligo rem nunc serio agi de novo Breviario edendo qua in re maximum mihi abs te præstitum est beneficium; duabus siquidem formis jam prælis rursus supposueram a quibus prosequendis nunc cessandum mihi visum est. Exemplaria bina tui Epiphanii a me recusi nuper misi, nunc alia duo etiam mitto si forte priora istuc non pervenerunt. Plura mitterem nisi caritas vecture me deterreret. Si quid sit in quo præstare queam tibi officium quæso indica, libentissime parebo. Vale vir admodum Revde. Ant. 22. Aug. 1588.

[From your letter of the 10 Kalend of June I understand that you are serious about the new Brevary to be published, which is a most great kindness to me; accordingly I have now put it again on the press in two formats. I have sent two printed copies of your Epiphanius recently, now I also send another two in case the earlier ones have perhaps not reached you. I might send more unless the cost to send them deters me. I beg you to tell me if I may be able to better serve you, most willingly I will obey. Farewell most reverend man.]

1481. - Jean Moretus to Gonçalo Ponce de Leon.
(Archives Plantiniennes, X, fo 246).
8 July 1589.

Illri Dno Gonçalo Ponce de Leon. Adi 8. Julij 1589.

Quæ ex adversa pagina descripta sunt Ill. ac Rme Dne, et Dno B. Ariæ Montano, socer meus Christophorus Plantinus scribenda dictaverat, sed proh dolor uti res humanæ instabilas singulis horis mutantur, nobis accidit nuperrime et detrimentum irreparabile. Die namque Smæ Trinitatis ex templo reversus, socer meus in graviorem incidit morburn qui ipsum non sine maximis doloribus lecto decumbantem detinuit, medici eosdem (ex apostemate in dextro latere comperint intrinsecus ex coacervatione phlegmatum exorto) productos dicebant qui licet post octo aut circiter dies cessare sunt visi, perdurante nihilominus febre, in dies ita diminuere vires corporis jam extenuati, ut resistere ultra non potuerit, tanta tamen animi tranquillitate quoscumque dolores ferens, ut incredibile quis existimavit, imo et consolando amicos ipsum in afflictionibus procumbentem consolari videbatur, mente, memoria et loquela ad extremum usque firma conservata, et ad rogata pauco tempore ante obitum aptissime respondens. Tandem postque ad prima usque Julij diem decubuisset ultima Junij hora decima aut circa sub noctem pueris lecto adstantibus eosdemque ita postremum est alloquutus: Pueri mei semper Mutuam Pacem Et Concordiam servate. Deinde etiam ipso fere quo obiit momento, Patri Matthiæ Societatis Jesu ad rogata, optime et aptissime respondit et sub extremæ vita finem tandem O Jesu dicendo, obdormire potius quam obire visus fait. Iste fuit optimi parentis exitus cujus animæ miseratur Deus. Detrimentum sane hoc nobis morte sua illatum resarcire nunquam poterimus nisi nobis Deus Opt. Max. auxiliumque amicorum nobis adsit, in quem spes et fiducia nostra collocanda est, ijsdem virtutibus quibus tantum nomen sibi comparavit (Constantia videlicet et labore) proviribus prosequendum. Interea, Vir Clarissme, humillime te rogamus ut benevolentiam illam tuam quam socero meo demonstrasti semper, cujusque nomine tibi hactenus plurimum semper debuimus et etiam nunc debemus, debebimusque semper, eandem inquam in hæredes etiam conservare digneris qui nos nostræque omnia ad obsequium D. T. humillime obferimus, Deum Opt. Max. rogantes ut anima optimi parentis defuncti sit propitius Teque diu Reip. Christianæ in aluven conservare dignetur.

[Moretus says that Plantin, after having dictated a letter to Arias Montano (a copy of which he includes), was seriously sick, and died quietly, the first of the month. Moretus tells in detail the last moments of his father-in-law, his great presence of mind, good-byes to his children. He hopes that Ponce de Leon will continue to show to Plantin's heirs the benevolence which he has always shown to Plantin.]

A third letter, from Plantin to Garnier (August 27, 1588), probably refers to Ponce de Leon's book (according to Voet, v.2, p.864):

1398. - Plantin to Garnier.
(Archives Plantiniennes, X, fo 239).
27 August 1588.

...Je vous prie recevoir aussi en gré le petit livret que je vous envoye dont la copie m'a esté envoyee de Rome par l'autheur de la version pour l'imprimer....

[I also ask you to accept the small booklet I am sending to you, a copy of which was sent to me from Rome by the author of the edition, to be printed...]

The copy sent from Rome may have been the first edition of Sancti Epiphanii ad Physiologum, printed in Rome in 1587, suggesting that Ponce de Leon wanted Plantin to reprint the book..