  We use 2MASS photometry to study colour-magnitude and colour-colour diagrams,
structure and mass distribution in the ionizing open cluster NGC\,6611.
Reddening variation throughout the cluster region is taken into account
followed by field-star decontamination of the CMDs. The field-star
decontamination showed that the lower limit of the main sequence (MS) occurs at
$\rm\approx5\,\ms$. Based on the fraction of Ks excess stars in the
colour-colour diagram we estimate an age of $1.3\pm0.3$\,Myr which is
consistent with the presence of a large number of pre-main sequence (PMS)
stars. The radial density distribution including MS and PMS stars is fitted by
a King profile with a core radius $0.70\pm0.08\,pc$. The cluster density
profile merges into the background at a limiting radius $6.5\pm0.5\,pc$. In the
halo and through the whole cluster the MFs have slopes $\rm\chi=1.52\pm0.13$
and $\rm\chi=1.45\pm0.12$, respectively, thus slightly steeper than Salpeter's
IMF. In the core the MF is flat, $\rm\chi=0.62\pm0.16$, indicating some degree
of mass segregation since the cluster age is a factor $\sim2$ larger than the
relaxation time. Because of the very young age of NGC\,6611, part of this
effect appears to be related to the molecular cloud-fragmentation process
itself. We detect $362\pm120$ PMS stars. The total observed mass including
detected MS (in the range $\rm5-85\,\ms$) and PMS stars amounts to
$\sim1\,600\,\ms$, thus more massive than the Trapezium cluster. Compared to
older open clusters of different masses, the overall NGC\,6611 fits in the
relations involving structural and dynamical parameters. However, the core is
atypical in the sense that it looks like an old/dynamically evolved core.
Again, part of this effect must be linked to formation processes.
