Insects associated with carrions are crucial in nutrient recycling and are of substantial importance in forensic entomology in the estimation of post-mortem intervals. This study presents an all-inclusive checklist of insects associated with slaughtered pig (Sus scrofa Linn.) carrions deposited in a grassland habitat at the University of Port Harcourt, Nigeria, over three consecutive years (2023–2025). Freshly euthanized (slaughtered) pig carrions were deposited during dry and rainy seasons and observed throughout decomposition stages (fresh, bloated, wet, and dry). Insects on the carrions were sampled with a sweep net and hand-picking techniques, preserved, and identified to the species level. The insect community comprises 22 species, 15 families, and 4 orders (Diptera and Coleoptera, Dermaptera, and Hymenoptera) with their arrival time matching unique decomposition stage(s). Calliphoridae, Muscidae, Sarcophagidae, and Ulidiidae families (Diptera) were the earliest and most abundant colonizers, while Staphylinidae, Histeridae, Cleridae, and Dermestidae families (Coleoptera) predominated during later stages. Seasonal variation influenced species richness, activity, and abundance, especially in the rainy season. The insect checklist of this study provides baseline data for the Southern region of Nigeria, and augments the growing body of forensic entomology in the tropics.