Polish minority in Slovakia (pre-1918 Hungary) was concentrated in the regions of Spis and Orava, which are today split between Poland and Slovakia. Data on the number of ethnic Poles in these areas before WW1 comes from Czech scholars Sembera, Polivka, Niederle and Pastrenk (for counties Liptó, Árva and Trencsén), Slovak scholars Misika and Czambela (for county Szepes) and Polish scholars Zawiliński, Smólski, Kołodziejczyk, Skawiński, Orłowicz (for Cadca district). There is also "Carte de la répartition de la population polonaise dans ses limites ethnographiques et sur les confins" from 1915.

That last of mentioned sources - map "Carte de la répartition de la population polonaise dans ses limites ethnographiques et sur les confins" from 1915 - gives the following percentages of Poles in each county: 50% for Árva, 30% for Szepes, 20% for Liptó and 16% for Trencsén.

1) Poles in County Trencsén:

According to Sembera and Pastrnek in year 1900 there were around 33,700 Poles in 13 towns and villages of the Csaca District in northern part of the Trencsén county. In addition to this, there were around 2,300 Poles in the city of Csaca itself.

So in total in 1900 there were 36,000 Poles in the Csaca District of the Trencsén county. Those 13 Polish settlements were:

Turzówka (Turzovka)
Rakowa (Raková)
Wysoka nad Kisucą (Vysoká nad Kysucou)
Maków (Makov)
Oleśna (Olešná)
Oszczadnica (Ócsad)
Podwysokie
Staszków (Staškov)
Zakopcze (Zákopcse)
Świerczynowiec (Svrčinovec)
Czerne (Cserne)
Skalite (Skalité)
Horzelica

According to Alois Votjech Sembera, "Mnoho-li jest Cechu, Moravanu a Slovaku a kde obyvaji", Vienna 1876, population of the Cadca district in Trencsén county at that time was 31,251 of whom 23,946 (77%) were Poles - but Sembera did not include population of villages Zakopcze, Maków and Wysoka, which were overwhelmingly Polish - if including also them, around 92% of the population were Poles. Czech scholar Frantisek Pastrenk in "O nareci polskem v horni stolici Trencinske” confirmed ethnic Polish character of that region. Roman Zawiliński who researched the Cadca District in years 1893-98 (travelling from village to village) confirmed Polishness of local inhabitants. In his book "Przyczynek do etnografii górali polskich w Węgrzech" published in 1910 he estimated the number of Poles in that region as 36,000 out of the total population of 40,038. Grzegorz Smólski who researched that region in 1903-1912 estimated the number of Poles as 36,000. Edmund Kołodziejczyk in "Ludność polska na Węgrzech" (1910) estimated that in 1900 there were 33,396 Poles (excluding the village of Zakopcze) out of 38,313 people, so 87% and 50% in the town of Cadca. Marek Skawiński included the village Zakopcze as well and arrived at 35,476 - 35,640 Poles, who were 93% of the total population. Mieczysław Orłowicz in 1913 estimated total population of Cadca Land as 50,318 including 47,000 (93%) Poles.

2) Poles in County Árva:

According to Sembera and Polivka, in 1900 there were around 30,600 Poles in 23 settlements of northern part of the Árva (Orava) county as well as around 2500 Poles in two other towns, and some number of Poles in other villages. In total around 34,000 Poles in Upper Orava in 1900.

3) Poles in County Szepes:

According to Sembera and Slovakian scholars Misika and Czambela, there were (in year 1900) at least 30,300 Poles in 50 villages (listed by name and by population size) in northern half of the Szepes county. Those 50 villages were almost fully Polish-inhabited. In addition to those 50 villages in a large number of other mixed German-Polish and Rusyn-Polish towns and villages Poles were around 50% of inhabitants and numbered at least 10,000.

So in total there were at least 40,000 Poles in northern part of the Szepes county in year 1900.

4) Poles in County Liptó:

According to Sembera and Niederle, there were 10 almost fully Polish settlements in Liptó county. They numbered in total almost 10,000 Poles in year 1900. In addition to that, there could also be some Polish individuals dispersed in other settlements.

5) Summary:

According to a 1919 Polish publication "Spisz, Orawa i okręg czadecki", there were at least ("conservative estimates") 180,000 Poles in Hungary, and at least 130,000 of them were concentrated in the areas of Polish settlement in Spis, Orava and Cadca (Csaca).