In order to analyze the associations between thyroid cancer and environmental factors, we analyzed the national sample cohort representative of the entire population provided by the Korean National Health Insurance Service database record from 2006 to 2015. The cohort was categorized according to age, body mass index, income, residential areas, frequency of exercise, frequency of alcohol drinking, diet, presence or absence of hyperthyroidism, presence or absence of hypothyroidism, and smoking data. Age ≥ 55 years (HR 0.68, 95% CI 0.53-0.88), lower income (0.57, 0.40-0.80), and current smoking (0.69, 0.55-0.85) were associated with lower thyroid cancer occurrence among men. Body mass index (BMI) ≥ 25 kg/m2 (1.51, 1.26-1.82), higher income (1.44, 1.19-1.76), urban residence (1.24, 1.03-1.49), and presence of hypothyroidism (3.31, 2.38-4.61) or hyperthyroidism (2.46, 1.75-3.46) were associated with higher thyroid cancer occurrence among men. Age ≥ 55 years (0.63, 0.56-0.71), moderate alcohol drinking (0.87, 0.77-0.99), and current smoking (0.56, 0.37-0.85) were associated with lower thyroid cancer occurrence among women. BMI ≥ 25 kg/m2 (1.41, 1.26-1.57), frequent exercise (1.21, 1.07-1.36), higher income (1.18, 1.06-1.32), urban residence (1.17, 1.06-1.29), and presence of hypothyroidism (1.60, 1.40-1.82) or hyperthyroidism (1.38, 1.19-1.61) were associated with higher thyroid cancer occurrence among women. In conclusion, age ≥ 55 years and current smoking were associated with lower thyroid cancer occurrence, while BMI ≥ 25 kg/m2, higher income, urban residence, hypothyroidism, and hyperthyroidism were associated with higher occurrence in both men and women.