Abstract: This study adopts a geo-linguistic approach. Specifically, it systematically investigates the geographical distribution, age-related variations, and their causes of lexical variants for sleep in Nantong dialects through field investigations and dialect mapping. It elucidates the spatio-temporal evolution patterns of three lexical systems: kùn/kùnjiào, hōujiào, and shuìjiào. Three main findings emerge from this study. Firstly,the kùn system shows the widest distribution in Nantong, which stems from a Wu Chinese substratum. This linguistic feature is a remnant of the area’s pre-Putonghua (modern standard Chinese) history. Nantong, though now assigned to the Jianghuai dialect zone, was once heavily influenced, or even populated, by speakers of Wu Chinese. Secondly, the hōujiào system, a dialectal innovation derived from verbalizing the onomatopoeic word hōu, is predominantly concentrated in northwestern Jiangsu, particularly in Rugao and Hai’an. This distribution is geographically significant, as its isogloss remarkably coincides with the Rutai Canal and historical administrative boundaries. Third, the shuìjiào system exhibits scattered diffusion among younger generations, significantly influenced by Putonghua promotion and educational policies.