What percentage of Greek Macedonians were Slavophones in the early 1900’s?

We have statistics published in a Belgian magazine from 1912 (De Godsdiensten op den Balkan.), just before the Balkan wars divided up Macedonia, and cited in Manastir Vilayet – Wikipedia and Salonica Vilayet – Wikipedia. Of course, the Ottoman Vilayets do not coincide with the modern borders: Salonica Vilayet is now 3/4 Modern Greece, 1/4 Bulgaria; Manastir Vilayet is 1/2 Greece, 1/2 FYRO Macedonia.

The stats in 1912 were:

• Salonica Vilayet: Orthodox Greeks: 168k, Orthodox + Muslim Bulgarians: 144k
• Manastir Vilayet: Orthodox Greeks: 62k, Orthodox + Muslim Bulgarians: 355k

As a result of the Balkan wars, Slavic-speakers in the part of the erstwhile Salonica Vilayet that was incorporated into Greece were subject to population exchanges with Bulgaria. As Niko Vasileas’ answer reports, that involved 66k Slavic-speakers; Slavic speakers of Greek Macedonia – Wikipedia puts the total from 1900–1920 at over 100k. People who read me here will be familiar with my constant quoting of The Tale Of The Stairs; its author, Hristo Smirnenski, was born in Kilkis (Bulgarian Kukush), now in Greece.

The Slavic-speakers in the part of the erstwhile Manastir Vilayet that was incorporated into Greece were not subject to population exchange, and they constitute the Slavonic-speaking minority present in Western Greek Macedonia.

Slavic speakers of Greek Macedonia – Wikipedia:

The 1928 census recorded 81,844 Slavo-Macedonian speakers or 1.3% of the population of Greece, distinct from 16,755 Bulgarian speakers. Contemporary unofficial Greek reports state that there were 200,000 “Bulgarian”-speaking inhabitants of Macedonia, of whom 90,000 lack Greek national identity. The bulk of the Slavo-Macedonian minority was concentrated in West Macedonia. The census reported that there were 38,562 of them in the nome of Florina or 31% of the total population and 19,537 in the nome of Edessa (Pella) or 20% of the population. According to the prefect of Florina, in 1930 there were 76,370 (61%), of whom 61,950 (or 49% of the population) lacked Greek national identity.

Of course, the 1928 census was conducted after the 1922 population exchanges, where Muslims in Greece were exchanged with Christians from Anatolia speaking Greek, Turkish, and in one idiosyncratic instance Bulgarian (Ἡλληνιστεύκοντος). The majority of arriving refugees settled in Macedonia, though the majority of departing refugees were also from Macedonia. So the proportions reported in the 1928 are likely smaller than they were in 1920.

That said, the prefectures of Florina and Pella were not traditionally Greek-speaking at all: the Greek–Slavic linguistic boundary ran south of them, halfway through Kastoria and Kozani, and most of Thessaloniki prefectures. (See the description in Sandfeld’s Linguistique Balkanique.) See e.g. https://upload.wikimedia.org/wik…