Maize grain yield is a function of dry matter accumulation and harvest index. However, it is difficult to explain grain yield QTL in terms of underlying physiological processes due to limitation of optimum recombinant inbred line (RIL) population size required and physical and financial constraint associated with measuring physiological traits. A novel approach exploiting identity-by-descent (IBD) enables phenotyping fewer lines without loss in precision or power for QTL identification. A population of 128 IBD limited RILs were developed from a sister line cross between CG60 and CG108 (both Iodent; 70% IBD; and significantly differing in grain yield) and each were crossed to CG102 (Stiff stalk). Field experiments were planted as an RCBD at three locations and two replications. Single factor analysis of variance was used to identify significant trait-marker associations. The IBD limited RILs exhibited a wide range of phenotypic variation for grain yield, from 94.1 to 141.4 bu/ac. Eight smaller effect grain yield QTLs were identified. The CG60 allele at bnlg105 (SSR marker, chromosome 1) and CG108 allele at umc1705 (SSR marker, chromosome5) gave a 13.5 bu/ac advantage over opposite allelic combination. The RILs with parental allele CG60/CG60, CG60/CG108, CG108/CG60, and CG108/CG108 for bnlg105 and umc1705 were selected. These 81 RILs and parent lines were crossed to CG102 and were planted in a three replication RCBD. Dry matter accumulation and harvest index will be measured at silking and physiological maturity stage to enhance our understanding of grain yield QTL and describe it in terms of its underlying physiological mechanisms. Results from this experiment will be discussed.