To identify the etiology of peripheral eosinophilia in a large pediatric population and to develop a diagnostic algorithm to help guide diagnosis and management of peripheral eosinophilia in the outpatient pediatric population. We performed a retrospective chart review of children presenting to Texas Children's Hospital in Houston with peripheral eosinophilia between January 1, 2011 and December 31, 2019. Eosinophilia was classified as mild (absolute eosinophil count AEC >500 and <1500 cells/μL), moderate (AEC >1500 and <4500 cells/μL), or severe (AEC >4500 cells/μL). Demographic information and diagnostic workup data were collected. A total of 771 patients aged <18 years were evaluated. The most common cause of eosinophilia was allergy (n = 357; 46%), with atopy (n = 296) and drug reaction (n = 54) the most common subcauses. This was followed by unknown etiology (n = 274; 36%), infectious causes (n = 72; 9%), and eosinophilic disorders (n = 47; 6%). Many patients with an unknown cause (n = 202; 74%) had limited or no follow-up testing. More information on the etiology of pediatric eosinophilia and workup data could help identify the causes. This study provides important information on the evaluation of eosinophilia in the US pediatric population, including a diagnostic algorithm to guide primary care pediatricians.