The collective dynamics of spin textures driven by thermal fluctuations offer a path to understanding many-body thermodynamics in solid-state systems and designing high-dimensional probabilistic computing devices. However, due to the difficulty in experimental observation, quantitative modelling of this phenomenon remains elusive. Here, we report a direct measurement of spatial correlations between long-range fluctuating domain walls in ultra-weakly pinned ferrimagnetic thin films. The correlation can be dynamically tuned by extremely weak magnetic fields at sub-µT level. The results reveal an unprecedented linear decay in correlation with the DW distance. We precisely reconstruct the energy landscape that enables the quantification of experimental studies of correlation using the Edwards–Wilkinson equation. Our work provides a quantitative understanding of collective dynamics and can be useful for implementing energy-efficient spintronics devices.