Relative success of maize (Zea mays L.) breeding programs depends on the proper choice of parental germplasm and the recognition and the use of heterotic groups. Our objective was to identify maize populations with exotic germplasm that would be potentially useful germplasm sources in temperate area maize breeding programs. A factorial mating design was used to produce 35 crosses between seven Iowa Stiff Stalk Synthetic and five non-Iowa Stiff Stalk Synthetic populations. The 12 parental populations and their 35 population crosses also were selfed to produce F2 generation. The two sets of genetic materials were evaluated at five Iowa locations for two years. Estimates of general combining ability (GCA) for each parental population and specific combining ability (SCA), heterosis (H) and inbreeding depression (ID) for each population cross were determined for grain yield. The population cross, BS10(FR)C14 by BS29(R)C3, had the greatest significant estimate of SCA (0.55* t ha-1), the greatest grain yield at the F1 (8.30 t ha-1) and F2 (6.71 t ha-1) generations, the lowest estimate of ID (1.59 t ha-1), but the estimate of H (1.90 t ha-1) was similar to the average estimate of H (1.74 t ha-1) for all crosses. BS10(FR)C14 is a selected strain within the Iowa Stiff Stalk Synthetic heterotic group, whereas BS29(R)C3 is an adapted strain of Suwan-1 a tropical cultivar that originated in Thailand. BSSS(R)C14 (0.63* t ha-1) and BS13(S)C9 (0.54* t ha-1), both selected strains of Iowa Stiff Stalk Synthetic, had the greatest estimates of GCA of all parental populations; BS10(FR)C14 had a significantly positive GCA estimate (0.25* t ha-1), which was similar in magnitude to the GCA estimates for BS11(FR)C14, BS29(R)C3, and BSCB1(R)C14 of the non-Iowa Stiff Stalk Synthetic heterotic group. The data provide information on the relative performance of the populations assigned to the respective heterotic groups of the U.S. Corn Belt, and that BS29(R)C3 includes germplasm that could enhance the genetic variation of the non-Iowa Stiff Stalk Synthetic heterotic group.