Abstract While the density profiles (DPs) of Lambda cold dark matter haloes obey the Navarro, Frenk & White (NFW) law out to roughly one virial radius, rvir, the structure of their outer parts is still poorly understood, because the one-halo term describing the halo itself is dominated by the two-halo term representing the other haloes picked up. Using a semi-analytical model, we measure the real-space one-halo number DP of groups out to 20rvir by assigning each galaxy to its nearest group above mass Ma, in units of the group rvir. If Ma is small (large), the outer DP of groups falls rapidly (slowly). We find that there is an optimal Ma for which the stacked DP resembles the NFW model to 0.1 dex accuracy out to 13 virial radii. We find similar long-range NFW surface DPs (out to 10rvir) in the Sloan Digital Sky Survey observations using a galaxy assignment scheme that combines the non-linear virialized regions of groups with their linear outer parts. The optimal Ma scales as the minimum mass of the groups that are stacked to a power 0.25–0.3. The NFW model thus does not solely originate from violent relaxation. Moreover, populating haloes with galaxies using halo occupation distribution models must proceed out to much larger radii than usually done.