Avian haemosporidian parasites provide a model system for understanding ecological and evolutionary host–parasite interactions. The diversity and distribution of these parasites remains incomplete, and, here, we provide the first range-wide assessment of avian haemosporidians in a continentally distributed host, the Northern Cardinal (Cardinalis cardinalis). Based on molecular techniques, we show geographical differences in prevalence and lineage diversity between host subspecies and identify several novel lineages. We use phylogenetic reconstruction to show where these lineages fit into the expanding evolutionary tree of avian haemosporidian lineages. All except 1 subspecies of Northern Cardinal are highly parasitized by a wide diversity of Plasmodium and Parahaemoproteus. Compared to published studies that used microscopy to determine prevalence in this host, we find a much higher number of infected individuals (67.4% vs. 45% or less). Consistent with previous studies, Parahaemoproteus from the Northern Cardinal was found to be highly host specific and geographically structured, whereas Plasmodium was less host specific and geographically unstructured.