This modern map of the ecclesiastical divisions of the Diocese of Chartres was published in the 1860's in the Memoires of the Societé archéologique d'Eure-et-Loir.

It is the work, I presume, of Lucien Merlet, who was then the Archiviste of the departément d'Eure-et-Loir, and, I also assume, was generated by him from a careful reading of the documents placed under his care, including, above all, the various detailed Pouillés (the occasionally-made, parish-by-parish census of the diocese), some of which Merlet had just published himself in his edition of the Cartulary of the Cathedral (all of the known pouillés were subsequently published by Auguste Longnon in his beautiful Academie des Inscriptions et Belles Lettres edition of the Pouillés de la Province de Sens (Recueil des Historiens de la France... Pouillés, IV, Paris, 1904).

From this map we can see that the diocese of Chartres was divided into six Archdeaconries: those of Blois, Vendôme, Châteaudun, Dreux, Poissy and the so-called "Grand Archdeaconry," centered around Chartres itself.

Within each of these the subdivision into deaconries varied somewhat.

Thus, the relatively small Archdeaconries of Blois and Vendôme were apparently without internal divisions, while that of Châteaudun was subdivided into deaconries of "Châteaudun in the Perche" (apparently centered at Authon?) and of Châteaudun proper.

And the Grand Archdeaconry in turn had deaconries based at Nogent[-le-Rotrou], Brou, Rochfort [-en-Ivelines], Courville[-sur-Eure], Épernon and Chartres itself; while the Archdeaconries of Dreux and Poissy were subdivided into two deaconries, based at Brezolles and Dreux, Meulan and Poissy, respectively.