Genetic diversity is essential for genome sequencing and a key contributor to increase frequency of favorable alleles for maize improvement. The objectives of this study were to determine the genetic components, assess the genetic diversity, and propose the heterotic grouping of a large sample of short-season maize populations based on multiple traits. Sixteen maize populations were included in a diallel mating design that followed Gardner-Eberhart Analysis (GEAN) II to estimate variety (vi) and heterosis (hij) genetic effects. The general combining ability (gi) estimates were also determined and used to classify the populations based on their genetic diversity. Data were generated in partially balanced single lattice experiments across North Dakota (ND) locations in 2010, 2011, and 2012. Combined analyses of variance showed significant differences among genotypes. Heterosis effects explained the most among diallel entries sum of squares for grain yield, while vi effects had greater influence on grain quality traits. The gi effects agreed with the genetic effect that had larger contribution to the total among diallel entries sum of squares for various traits. Three groups were formed based on the genetic distances (GD) of the gi estimates. Four heterotic groups were established based on sij estimates for grain yield. Close correspondence was observed between the groups formed using GD and sij. The heterotic grouping among populations agreed with their genetic background information and heterotic group’s specific and general combining ability (HSGCA) estimates. The EARLYGEM 21 populations having exotic background were assigned to a unique heterotic group. The heterotic groups established among these populations will increase breeding efficiency to improve and develop genetically broad-based populations. Inter-population recurrent selection programs can be employed for population crosses with high grain yield and above average grain quality formed by parental populations belonging to different heterotic groups. Intra-population recurrent selection programs can also be established for the parental populations identified with desirable grain quality traits. These populations will serve as unique germplasm sources of short-season diverse inbred lines to produce the next generation of diverse northern U.S. hybrids. New heterotic patterns have been established as a source of new commercially viable single-cross and population hybrids. [Full abstract in document contains symbols]