Complete blood cell counts have been used as a diagnostic tool across many animal species including swine. To investigate the factors that cause variation in complete blood cell count results, a total of 2,284 whole blood samples were collected from 2012 to 2019 in preweaning piglets (n = 518), nursery pigs (n = 1,704), and grower pigs (n = 60). Whole blood was collected into K2EDTA blood collection tubes and assayed using an automatic hematologic analyzer within 6 hours of collection. Data were analyzed by Mixed procedure of SAS with gender, parity group, and farrowing season as fixed effects. Body weight and age of pigs served as covariances. Farrowing season was grouped into summer (born during May to October) or winter (or November to April). Pigs that were born from first, second, and third parity, and four and above parity sows were assorted into parity group 1, 2 to 3, and 4+, respectively. Barrows had a greater concentration of total white blood cells (P < 0.01), lymphocytes (P < 0.01), and neutrophils (P < 0.01) compared to gilts. Barrows had lower mean corpuscular volume (P = 0.03), mean corpuscular hemoglobin (P < 0.01), and mean corpuscular hemoglobin concentration (P = 0.02) compared to gilts. Pigs that were farrowed in the winter season had a greater concentration of white blood cells (P = 0.01), neutrophils (P = 0.01), and the percentage of neutrophils (P = 0.03), but were lower in the percentage of lymphocytes (P = 0.03) compared to pigs farrowed during summer. Pigs born to parity four and above sows obtained a greater lymphocyte count (P = 0.01), percentage of neutrophils (P = 0.02), and percentage of lymphocytes (P = 0.01). We concluded that peripheral complete blood cells count results were affected by gender, farrowing season, and sow parity.