The vulnerable groups are the most prone to the menace of food insecurity. Yet, there exists a dearth of information on their dietary diversity and food security status. This study, therefore, assessed the food security status of the vulnerable group of Fadama III additional financing in Nigeria using cost-of-calories, logit model, household dietary diversity score and Tobit model. The results revealed that the vulnerable group are aged, smallholder farmers who live on a low average monthly income of N13,718 (USD 37.13). The majority (88.5%) were food insecure while only 11.5% meet the daily calorie intake of 2260kcal per capita. Educational level, income and value of productive assets positively influenced their food security status while the household size had a negative impact. The majority of the vulnerable group had low dietary diversity between 0.31 to 0.40 portraying poor nutrition among the vulnerable group. The determinants of food dietary intake are gender, educational level and household size. The highly employed food insecurity coping strategy are allowing children to eat first, collecting food from the wild, selling assets to buy food, eating once a day and buying food on credit. This study suggests policy measures for educating and provision of better family planning for the vulnerable group to enhance dietary diversity and food security.