Knowledge on the physiological and genetic processes determining kernel weight (KW) in maize is critical. However, little is known about the genetic control of KW and its component traits (kernel growth rate, KGR, and grain-filling duration, GFD).  We phenotypically characterized 245 RILs from the IBM4 population (B73xMo17) under contrasting growth environments, and a QTL analyze was done for grain-filling traits. We were specifically interested in testing if known phenotypically correlated traits, like kernel maximum water content (MWC) and KGR, do have a similar genetic basis. All traits had a significant G x E interaction (p<0.001), and showed consistent transgressive segregation. Genetic and environmental KW variability was explained by both KGR and GFD differences. As expected, KGR was highly related to MWC, and GFD was related to the kernel desiccation rate and negatively correlated with kernel moisture concentration at physiological maturity (MC-PM). A total of 25 and 21 QTLs were detected at each environment across traits. Most detected QTLs presented small effects, generally being the alleles from B73 the ones improving trait values. Several QTLs for KW co-localized with QTLs for KGR and MWC, but no QTL for KW co-localized with QTLs for GFD or MC-PM. Moreover, KGR and GFD showed no common QTLs, evidencing independent genetic control.  Epistatic effects were not detected, and only six QTLs showed no QTL x E interaction. Some of these constitutive QTLs pointed specific candidate genes for future research. Results showing the co-localization of QTLs for KGR and MWC evidence the common genetic basis that known phenotypically correlated traits do have at the field level.