There is first the TLFI’s definition to guide us.

(TLFi) Entendre parler de qqn, de qqc. : Avoir des nouvelles de quelqu’un, être informé de quelque chose.

• Je serais venu sûrement, si j’avais entendu parler d’un crime dans le quartier. (ROMAINS, Hommes bonne vol., 1932, p. 134)
• Vous n’entendriez plus parler de moi, si vous le désiriez. (MONTHERL., J. filles, 1936, p. 1001)

There is then the internaut‘s definition.

Entendre ce que l’on dit sur une personne ou sur une chose, écouter les rumeurs.
Traduction en anglais : to hear about.

Dictionaries are essential for the preservation of a language but they all seem to be now and again insufficient. This is the case for these définitions.

Do not apply :

• avoir des nouvelles de qqn.
• être informé de qqc.
• entendre ce que l’on dit sur une chose
• écouter les rumeurs

If you were to translate “entendre parler de” as it occurs in your text you’d use “hear about”.

• Non. J’en ai déjà entendu parler de cette région du Nord Ouest de la France, mais je n’ai jamais eu l’occasion d’y aller.
  No. I heard about this north-western region of France, but I never happened to go there/to visit it.

To say that another way in French (“J’ai déjà entendu parler de cette région”), you could say “Je connais un peu cette région d’après ce qu’en disent les gens” or “Je connais cette région par ouï-dire“. I must repeat that the four possibilities shown above do not apply in this context.

There is a difficulty in the usage of “en”; this usage is a case of what is called “redondance expressive”; “en” stands for “région” and so there are two “coi” in this sentence and both represent the same thing. It is used, among other things, in order to be more assertive; you don’t have to use it though.

• Non. J’ai déjà entendu parler de cette région du Nord Ouest de la France, mais je n’ai jamais eu l’occasion d’y aller. Julie: Côté nature, c’est magnifique, et ça s’embellit avec le temps.

Some additional points concerning the redundancy usage for “en”

There exists a variety of connotations associated with this usage (“redondance expressive”) and my feeling is that it is a colloquial usage, mostly. Moreover, the range of possibilities, which I do not fathom, might border into the otiose, where one is not sure to recognise a real added meaning, and that’s a problem causing much dicussion.

I am nevertheless quite sure about two of the aspects that this redundancy can render and I use an example that figures in another of my answers to explain that. It happens that from this unique example can be exacted the two ideas. I should add that the mere matter-of-fact uttering of this sentence is not sufficient to impart what is meant to the interlocutor. Precise intonations that I am far from mastering myself are necessary, otherwise you could just fall flat on your face in a try to convey the mentioned connotations by means of this sort of utterance. Let’s conclude these spoken language matters with a reassuring note; there is no real necessity of a particular manner of elocution in the sentence under discussion; “J’en ai entendu parler” can be said quite normally; this is not independent of an impression that there is no well defined connotation to be extracted from the usage here, at most some faint added assertiveness maybe. This is also to insist that a special pronunciation is not very often needed (or at least used); the two cases I could remember clearly are somewhat exceptional.

• Ils en ont mangé des pommes !

Its meaning can be “I assure you that they ate apples.” or simply “They ate a lot of apples.”. Necessarily, the discussion preceding those words must have been about people eating apples or there must exists a context of common knowledge about apples; you can’t just start talking using it.

• — Alain me dit qu’ils n’ont pas touché aux pommes.
  — Ils en ont mangé des pommes ! Il n’y a aucun doute !

• Ils y avait un pommier avec d’excellentes pommes dans le jardin et les enfants les adoraient. Ils en ont mangé des pommes… il leur arrivait d’en abuser tellement qu’il ne mangeait plus rien à table.

“Redondance expressive” is treated in “Le Bon Usage, 14th edition” § 373, p. 465 and in the subsequent editions. This turn involving repetition is contested by certain people and found to be inelegant by others, not in the cases that were just dicussed but in certain cases when nothing evident seems to result from that usage, wherefrom the useleness referred to above. I join the url of the fourteenth edition below.
https://ia800206.us.archive.org/27/items/LeBonUsagefrenchpdf.com/Le_bon_usage%28frenchpdf.com%29.pdf