This study assessed the magnitude and frequency analyses of rainfall amounts and rainy days in Southwestern Nigeria, using 31 years daily rainfall data strategically collected for Ikeja, Ibadan, and Ilorin to represent the north/south dichotomy of the area. While the rainfall onset, retreat, and length of the growing season were determined using the percentage cumulative mean rainfall model emphasized by Odekunle et al. (2006), rainfall magnitudes (light, moderate, and heavy), rainy and rainless days’ thresholds were determined using Olaniran (GeoJournal 22:99–107, 1990) and Garbutt et al. (Arch Meteor Geophys Bioclim Ser B (35):143–159, 1981) approaches. Light rainfall among the three magnitudes recorded the highest frequency in all the years except in Ibadan in 1986 and 1989 when it had (40%) and (45%) against the closest moderate magnitude (56%) and (49%). Also observed are more downward trends in the frequencies of light, moderate, and heavy rainfall magnitudes. The frequency of maximum consecutive rainy and rainless days during the growing season in the locations witnessed upward trends between 1985 and 2015 only in Ikeja. Although, some of these parameters exhibited upward trends, which may be an advantage for agricultural productivity, however, the downward trends displayed by others may be unpalatable for food security in the region.