The butterfly (Lepidoptera) fauna of east-central Illinois is largely undocumented. We collected butterflies and examined specimens in the Insect Museum at Eastern Illinois University for unpublished records for five counties in east-central Illinois. Here we report 105 new butterfly county records: 17 for Clark County, 30 for Coles County, 28 for Cumberland County, 9 for Douglas County, and 21 for Edgar County. We also describe behavioral observations, in particular those behaviors related to reproduction, for some of the records. Of special note were two rare vagrants from Coles County found in the museum collection, the orange-barred sulphur (Phoebis philea) and the marine blue (Leptotes marina).