Strategic intensification through increased planting density is a cornerstone of maize yield enhancement in China. However, a comprehensive analysis of the nationwide spatiotemporal patterns in planting density and their association with on-farm yield remains limited. Here, we analyzed 95,040 farmer-plot surveys across 264 counties (2009-2023) to quantify density dynamics and yield associations across five agroecological regions. Nationally, the average planting density increased significantly from 54,300 to 62,200 plants ha(-1) over 15 years (+14.55%; P < 0.01), with an annual growth rate of 353 plants ha(-1). We found marked and persistent regional disparities, with current densities (2019-2023) ranging from 49,574 plants ha(-1) in the Southwestern Maize Region (SWM) to 69,921 plants ha(-1) in the Northwest Irrigated Maize Region (NWIM). The increase in yield response per 1,000 plants ha(-1) increase varied significantly (P < 0.05) among regions, reaching the highest level in NWIM (130 kg ha(-1)) and lowest in the Northern Spring Maize Region (NSM; 60 kg ha(-1)). The Huang-Huai-Hai Plain Summer Maize Region (HPSM), Northwest Dryland Maize Region (NWDM), and SWM showed intermediate responses of 100, 120, and 80 kg ha(-1), respectively. Our findings delineated the current and realized thresholds for intensification across China's agroecosystems, suggesting a practicable density range of 62,000-80,000 plants ha(-1) under prevailing management, with a yield gain potential of 60-130 kg per 1,000 plants ha(-1). To advance towards sustainable intensification, we propose region-specific optimization, scale-appropriate technologies, and institutional innovations to overcome smallholder fragmentation.