Background The incidences of atrial fibrillation (AF) and chronic kidney disease (CKD) are increasing, and AF is prevalent in patients with CKD. However, few studies have investigated the incidence or association of AF in a large CKD population from a longitudinal study. Methods and Results From a nationwide cohort, a total of 4 827 987 Korean individuals without prior AF, who received biennial health checkups provided by the National Health Insurance Service between 2009 and 2012 in Korea, were analyzed. Incidence of AF was ascertained through the end of 2018. During a median follow-up of 8.1 years, the annual incidence rate of AF was 1.17 per 1000 person-years among subjects without CKD, 1.55 for stage 1 CKD, 1.86 for stage 2 CKD, 2.1 for stage 3 CKD, and 4.33 for stage 4 CKD. In Fine-Gray regression models, CKD was associated with an increased risk of AF; the adjusted hazard ratios and 95% CIs of AF occurrence were 1.77 (1.69-1.85), 1.85 (1.80-1.91), 1.99 (1.95-2.04), and 4.04 (3.07-5.33) in individuals with CKD stages 1, 2, 3, and 4, respectively, compared with non-CKD. The association between CKD and incident AF remained statistically significant after adjustment for multiple confounding factors and was consistent across subgroups stratified by sex and age. Conclusions CKD is associated with an increased incidence of AF. Even mild CKD is associated with incident AF, and there was a stepwise increase in the risk of incident AF with a decrease in renal function.