Rapid growth in infancy has been shown to adversely affect iron status up to 1 year; however the effect of growth on iron status in the second year of life has been largely unexplored. We aimed to investigate the impact of growth and body size in the first 2 years on iron status at 2 years. In the prospective, maternal-infant Cork BASELINE Birth Cohort Study, infant weight and length were measured at birth, 2, 6, 12, and 24 months and absolute weight (kg) and length (cm) gain from 0 to 2, 0 to 6, 0 to 12, 6 to 12, 12 to 24, and 0 to 24 months were calculated. At 2 years (n = 704), haemoglobin, mean corpuscular volume, and serum ferritin (umbilical cord concentrations also) were measured. At 2 years, 5% had iron deficiency (ferritin < 12 µg/L) and 1% had iron deficiency anaemia (haemoglobin < 110 g/L + ferritin < 12 µg/L). Weight gain from 6 to 12, 0 to 24, and 12 to 24 months were all inversely associated with ferritin concentrations at 2 years but only the association with weight gain from 12 to 24 months was robust after adjustment for potential confounders including cord ferritin (adj. estimate 95% CI: -4.40 [-8.43, -0.37] µg/L, p = .033). Length gain from 0 to 24 months was positively associated with haemoglobin at 2 years (0.42 [0.07, 0.76] g/L, p = .019), only prior to further adjustment for cord ferritin. To conclude, weight gain in the second year was inversely associated with iron stores at 2 years, even after accounting for iron status at birth. Further examinations of iron requirements, dietary intakes, and growth patterns in children in the second year of life in high-resource settings are warranted.