  We present a sample of supernovae Type IIn (SNe IIn) from the untargeted,
magnitude-limited surveys of the Palomar Transient Factory (PTF) and its
successor, the intermediate PTF (iPTF). The SNe IIn found and followed by the
PTF/iPTF were used to select a sample of 42 events with useful constraints on
the rise times as well as with available post-peak photometry. The sample SNe
were discovered in 2009-2016 and have at least one low-resolution
classification spectrum, as well as photometry from the P48 and P60 telescopes
at Palomar Observatory. We study the light-curve properties of these SNe IIn
using spline fits (for the peak and the declining portion) and template
matching (for the rising portion). We find that the typical rise times are
divided into fast and slow risers at $20\pm6$ d and $50\pm11$ d, respectively.
The decline rates are possibly divided into two clusters, but this division has
weak statistical significance. We find no significant correlation between the
peak luminosity of SNe IIn and their rise times, but the more luminous SNe IIn
are generally found to be more long-lasting. Slowly rising SNe IIn are
generally found to decline slowly. The SNe in our sample were hosted by
galaxies of absolute magnitude $-22 \lesssim M_g \lesssim -13$ mag. The
K-corrections at light-curve peak of the SNe IIn in our sample are found to be
within 0.2 mag for the observer's frame $r$-band, for SNe at redshifts $z <
0.25$. By applying K-corrections and also including ostensibly "superluminous"
SNe IIn, we find that the peak magnitudes are $M_{\rm peak}^{r} =
-19.18\pm1.32$ mag. We conclude that the occurrence of conspicuous light-curve
bumps in SNe IIn, such as in iPTF13z, are limited to $1.4^{+14.6}_{-1.0} \%$ of
the SNe IIn. We also investigate a possible sub-type of SNe IIn with a fast
rise to a $\gtrsim 50$ d plateau followed by a slow, linear decline.
