The objectives of this study were to investigate variations in the milk composition and somatic cell count (SCC) from dairy cooperatives in Northern Thailand from January 2017 to December 2021. Milk composition among dairy cooperatives was also compared. The dataset included monthly milk composition (total solid (TS)%, fat%, protein%, lactose%, solid not fat (SNF)% and SCC) data from 15 dairy cooperatives, 2 private organizations, and their milk collection centers (1,800 records) collected in five provinces, including Chiang Mai, Chiang Rai, Lampang, Lamphun, and Phrae. The seasons were cold season (November to February), hot season (March to June), and rainy season (July to October). The dataset was compared among dairy cooperatives using a general linear mixed model. To detect a correlation, spearman correlation coefficients were calculated between SCC and milk composition. Results showed that the season significantly affected milk composition. The hot season appeared as the most critical season for all the parameters examined, showing the significantly lowest values (P < 0.001) of TS (12.33±0.3%), fat (3.79±0.27%) and protein (3.02±0.07%) whereas, a significantly highest SCC was obtained in the rainy season (321.21±3.93 x 1,000 cell/ml). Milk collecting centers of dairy cooperatives located in many districts had significantly different milk composition and SCC values. Lactose is the milk component that undergoes the greatest variation in response to the increase in SCC. This study highlighted the variations influencing milk composition and provided information for stakeholders and their roles in the dairy sector at the farm, dairy cooperative, and provincial levels.