An older man from the mid-Southeastern USA presented with acute onset of fever, fatigue, and non-bloody diarrhoea. There was high suspicion for tick-borne illness given exposure history, clinical presentation and laboratory abnormalities. Despite prompt treatment with doxycycline, the patient clinically worsened. He was diagnosed with secondary hemophagocytic lymphohistiocytosis (HLH) due to Heartland virus (HRTV). This is the second documented case of secondary HLH due to HRTV, and the first in a relatively immunocompetent patient. Furthermore, though HRTV has been primarily concentrated in the Central USA, our case provides evidence of further geographic expansion of HRTV, mirroring the increased range of the Lone Star tick. Clinicians should consider HRTV when a patient with a clinical presentation consistent with tick-borne illness fails to respond to doxycycline. Furthermore, healthcare providers should be aware of the geographic expansion of HRTV and the potential of HRTV to lead to secondary HLH.