Newcastle disease (ND) is a viral infection with a global distribution that poses significant economic implications and a serious threat to nutritional security. This highly contagious disease is often marked by high morbidity and mortality rates, creating a substantial public health risk. Consequently, identifying effective alternative diagnostic methods, such as the Enzyme-Linked Immunosorbent Assay (ELISA), is crucial for the early detection and control of ND. The aim of this study was to estimate the seropositivity of Newcastle disease virus (NDV) by comparing the sensitivity of Hemagglutination Inhibition (HI) and ELISA tests among 800 free-range chickens across four regions in Sierra Leone. Our findings revealed a higher seropositivity rate using the ELISA test (13.9%) compared to the HI test (9.8%). The eastern region was found to be the most affected, with seropositivity rates of 43.6% for ELISA and 42.3% for HI. Among the risk factors assessed, chickens aged one year and older (ELISA = 11.2%, HI = 11.7%) and male chickens (ELISA = 19.1%, HI = 13.0%) were identified as the most susceptible groups. This study concludes that the ELISA technique demonstrates superior sensitivity for the serological detection of ND virus, while also being less labor-intensive and time-consuming than traditional methods. The high seropositivity rates indicate widespread exposure to NDV in the country. To effectively control the disease, we recommend enhancing community awareness, improving husbandry practices, and implementing regular vaccination programs. These measures are essential to mitigate the impact of Newcastle disease on poultry health and local food security.