Elite germplasm and adequate genetic variation are essential in successful plant breeding programs.Maize (Zea mays L.) breeding programs in the U.S. Corn Belt have realized significant genetic advance with a limited sample of the available maize germplasm. The objective of our study was the incorporation of elite subtropical and tropical germplasm into elite U.S. Corn Belt germplasm. Crosses, backcrosses, and testcrosses were evaluated to identify superior progenies that were intermated to form germplasm sources that include 75% temperate germplasm and either 25% subtropical or 25% tropical germplasm. Backcrosses (25%) and testcrosses (12.5%) with 25% exotic germplasm had maturities and agronomic traits similar to the elite temperate germplasm sources. The populations formed by intermating the superior backcross progenies, based on backcross and testcross data, will provide additional germplasm resources for future use in temperate maize breeding programs.