Association analysis to identify genes and alleles underlying quantitative genetic variation is growing in value as the density of genotypic data increases. Association panels are often chosen to maximize molecular and phenotypic diversity, but traits measured at harvest require restricted phenology to obtain data on plants that mature within a comparable interval. The objective of this study was to characterize a set of inbred lines that will mature reliably in the upper midwestern United States for the purpose of assessing traits relevant to grain and stover yield as well as stover quality. A total of 1411 lines from the North Central Regional Plant Introduction Station, our program, and contributed by collaborators were grown in observation plots. A set of 627 lines were chosen based on fl owering within the desired interval, production of viable seed, agronomic suitability, uniformity, and pedigree information. Flowering time ranged from 944 to 1645 growing degree days (GDD). Genotypic data for the 627 lines was obtained using a 1536 Illumina Golden- Gate assay. The panel offers deep replication of most Midwest dent alleles. There is a lesser representation of tropical alleles relative to other association panels but includes some Germplasm Enhancement of Maize (GEM)-derived lines and early fl owering lines of tropical origin. The information described in this manuscript is anticipated to facilitate the use of this material for association genetic studies.