  In order to understand the physical properties of the series of organic
conductors $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]$X$ with $X$ = Cl, Br, and I,
not only electronic correlations but also the effect of disorder has to be
taken into account. While for Cl- and Br-containing salts the influence of both
parameters were investigated and a universal phase diagram was proposed, the
position of $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]I is still not settled. Here we
have conducted transport, infrared, and dielectric measurements on single
crystals of the title compound to clarify its electronic state at low
temperatures. The correlation strength was determined as $U/W \approx 2.2$;
thus this salt is placed deeper in an insulating state compare to the two
sister compounds. We found that inherent disorder leads to a Coulomb localized
insulating state similar to the moderately x-ray-irradiated
$\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl.
