Preharvest sprouting (PHS) of wheat occurs when the seeds germinate on the plant before harvest, resulting in reduced grain quality. The control of pre-harvest sprouting resistance involves several genetic factors, particularly those related to seed dormancy. Therefore, seed dormancy management is essential to seed agriculture and industry. In this study, we aimed to identify quantitative trait loci (QTLs) associated with dormancy and germination. QTL mapping was performed on a population of 166 backcrossed recombinant inbred lines (BILs) derived from a cross between the Japanese wheat cultivar “Norin 61” and the synthetic wheat line Syn32. This synthetic wheat line was developed by crossing the tetraploid wheat cultivar “Langdon” and a wild wheat species Aegilops tauschii accessions KU-2039. Germination was evaluated after two months of harvesting. Fifteen seeds from each individual were evaluated for seven days. A count of germinated seeds was conducted every 24 hours during the seven days. The excel tool Advanced Seed Germination Measurements was used to calculate germination percentage and germination index. Dormant lines were selected based on germination percentages and retested after 25 days. This procedure was repeated three times. Finally, eight genotypes with different degrees of dormancy; two with low dormancy levels, one with a medium dormancy level, and five with high dormancy levels were identified. DNA was extracted from young seedling leaves using the CTAB method, and genotyping was performed on the GRAS-DI platform. The study identified one major QTL for seed dormancy on chromosome 5D spanning the region from 337.70 to 339.70 Mbp, explaining 32.8% of the total phenotypic variation in seed dormancy. This is the first time that seed dormancy QTLs mapped in wheat chromosome 5D.