A total of 143 new USA state and Canadian province records of mayfly species are given based on initial published data. One hundred species and 34 states and provinces are represented in the new data. The most cited species (with four or more new state and provincial records each) include Acentrella nadineae, Iswaeon anoka, Leucrocuta maculipennis, Paracloeodes minutus, Procloeon viridoculare, and Pseudocentroptiloides usa. The most cited regions (with five or more new species records each) include Georgia, Indiana, Kansas, Kentucky, Maryland, Massachusetts, Michigan, Mississippi, Montana, North Carolina, Ohio, and Vermont. While the first record of Spinadis simplex is given for Arkansas, the former incorrect Arkansas record for the latter is shown to be attributable to Raptoheptagenia cruentata.