Background Rising poisoning incidences worldwide, primarily in developing countries, remain ambiguous due to paucity of data and poison centres. This study evaluates patterns and factors causing poor outcomes in Kiambu County, Kenya. Methods A records-based retrospective cross-sectional study of poisoning cases who presented to nine facilities between June 2015 and July 2020 was conducted. The data collected was analysed through descriptive, bivariate, and multivariate logistic regression using STATA version 13. Results Kiambu county has a minimum prevalence of poisoning of 3.2%. A total of 434 cases were studied. Most cases (85.5%) resulted from acute exposures, with 75% being intentional. Pesticides (61.1%), paraffin (18.7%), alcohol (6.5%), and pharmaceutical drugs (4.4%) were the primary poisons used. 3.9% didn't fit these categories, while 5.5% remained unknown. Common presentations at admission were vomiting (35.3%) and unconsciousness (21.6%). Pesticides were responsible for 72.0% of deaths. Sequelae occurred in 7.8%, full but delayed recovery in 17.6%, and 6.0% died. The largest cluster of total cases was found in Thika town sub-county. It also contained the primary clusters of alcohol and pesticide poisoning. Being male (AOR 4.577, 95% CI [1.244–16.842]) was significantly associated with adverse outcomes. Regardless of the poison, the majority 78.8% made a full recovery. Conclusion Due to the lack of standardized poisoning data tools, patient records lack vital information reflecting the quality of care that the patient received, reflecting a lack of structures to collect, analyse and utilise poisoning data for decision making. This study underpins the need for the establishment of a PC in Kiambu county, Kenya.