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The dimorphic mycoses (DM) of the United States, Histoplasma, Coccidioides, and Blastomyces, commonly known as endemic mycoses of North America (in addition to Paracoccidioides), are increasingly being diagnosed outside their historical areas of endemicity. Despite this trend, the maps outlining their geographical distributions have not been updated in more than half a century using a large, nationwide database containing individual patient-level data.Retrospective analysis of >45 million Medicare fee-for-service beneficiaries from 1 January 2007 through 31 December 2016. Diagnoses of histoplasmosis, coccidioidomycosis, and blastomycosis were defined by International Classification of Diseases 9th/10th edition codes. Primary outcome was the incidence of histoplasmosis, coccidioidomycosis, and blastomycosis for each US county. Clinically meaningful thresholds for incidence were defined as 100 cases per 100,000 person-years cases for histoplasmosis and coccidioidomycosis and 50 cases for blastomycosis.There were 79,749 histoplasmosis, 37,726 coccidioidomycosis, and 6,109 blastomycosis diagnoses in unique persons from 2007-2016 across 3,143 US counties. Considering all US states plus Washington DC, 94% (48/51) had at least one county above the clinically relevant threshold for histoplasmosis, 69% (35/51) for coccidioidomycosis, and 78% (40/51) for blastomycosis.Persons with histoplasmosis, coccidioidomycosis, and blastomycosis are diagnosed in significant numbers outside their historical geographic distributions established more than 50 years ago. Clinicians should consider DM diagnoses based on compatible clinical syndromes with less emphasis placed on patient’s geographic exposure. Increased clinical suspicion leading to a subsequent increase in DM diagnostic testing would likely result in fewer missed diagnoses, fewer diagnostic delays, and improved patient outcomes.