The aim of the study was to compare the course of Corylus pollen season in 2019 in 12 cities located in different regions of Poland: Szczecin, Bydgoszcz, Zielona Gora, Wroclaw, Opole, Sosnowiec, Cracow, Piotrkow Trybunalski, Warsaw, Lublin, Olsztyn, and Bialystok. The analyses were carried out with the volumetric method using Burkard or Lanzoni pollen samplers. The length of the pollen season was determined with the 95% method. The earliest onset of the season was recorded in Warsaw and Szczecin, and at the latest beginning was noted in Lublin. The highest maximum concentrations of Corylus pollen were recorded in Lublin (244 P/m3), while Olsztyn (65 P/m3) as well as Bialystok and Bydgoszcz (66 P/m3 in each) were characterized by the lowest values. The maximum daily concentration of Corylus pollen grains was recorded in 3 cities in the second decade of February (16–19.02) and in the other eight cities in the third decade of February (24–28.02). The exception was Bialystok, where the peak value was only noted on 5.03. The annual pollen sum reached the highest values in Lublin (1301 grains) and Wroclaw (1031 grains). The highest risk of allergy in individuals sensitive to the pollen of this taxon was found in Lublin, Wroclaw, and Piotrkow Trybunalski. In Lublin, the highest hazel pollen concentrations were recorded in the earlier years of the investigations as well.