This research assesses the impact of land use changes on Land Surface Temperature (LST) in Lahijan County, utilizing remote sensing data and a Geographic Information System (GIS) from 2000 to 2025. Land use change analysis indicates a significant decrease of 17.8% (24.71 km²) in forest areas and an increase of 24.17 km² in agricultural lands. However, the transition matrix reveals the conversion of 3.28 km² of prime agricultural land to built-up areas and 1.13 km² of forests to agricultural lands, illustrating phenomena of rural encroachment and gentrification. Regional thermal analysis showed that built-up and barren lands had the highest average temperatures (mean LST for built-up areas in 2025: 29.90°C), while forests exhibited the most stable and coolest thermal behavior (0.5 to 1.5°C cooler than anthropogenic surfaces). A strong and significant linear correlation was observed between the increase in built-up land area and the intensity of the Urban Heat Island (UHI) effect, with the UHI intensity rising from 0.06°C in 2000 to 1.37°C in 2010. Spatial analysis using Moran’s I (Moran’s I = 0.976) and Local Indicators of Spatial Association (LISA) confirmed a clustered pattern of LST distribution with high spatial autocorrelation. Thermal hot spots were not only found in urban areas but also extended along roads and in rural settlements that had undergone land use changes, whereas cold spots precisely corresponded with forested regions. The findings suggest that land use changes, including the conversion of forests and agricultural lands into impervious surfaces, have led to reduced albedo and evapotranspiration, consequently increasing sensible heat flux. This physical process is the primary driver of micro-heat island formation in rural areas and the intensification of the heat island effect in Lahijan, underscoring the importance of land use planning for mitigating thermal impacts.