  We present results from a systematic infrared (IR) census of R Coronae
Borealis (RCB) stars in the Milky Way, using data from the Palomar Gattini IR
(PGIR) survey. R Coronae Borealis stars are dusty, erratic variable stars
presumably formed from the merger of a He-core and a CO-core white dwarf (WD).
PGIR is a 30 cm $J$-band telescope with a 25 deg$^{2}$ camera that surveys
18000 deg$^{2}$ of the northern sky ($\delta>-28^{o}$) at a cadence of 2 days.
Using PGIR J-band lightcurves for $\sim$60 million stars together with mid-IR
colors from WISE, we selected a sample of 530 candidate RCB stars. We obtained
near-IR spectra for these candidates and identified 53 RCB stars in our sample.
Accounting for our selection criteria, we find that there are a total of
$\approx350^{+150}_{-100}$ RCB stars in the Milky Way. Assuming typical RCB
lifetimes, this corresponds to an RCB formation rate of 0.8 - 5 $\times$
10$^{-3}$ yr$^{-1}$, consistent with observational and theoretical estimates of
the He-CO WD merger rate. We searched for quasi-periodic pulsations in the PGIR
lightcurves of RCB stars and present pulsation periods for 16 RCB stars. We
also examined high-cadenced TESS lightcurves for RCB and the chemically
similar, but dustless hydrogen-deficient carbon (dLHdC) stars. We find that
dLHdC stars show variations on timescales shorter than RCB stars, suggesting
that they may have lower masses than RCB stars. Finally, we identified 3 new
spectroscopically confirmed and 12 candidate Galactic DY Per type stars -
believed to be colder cousins of RCB stars - doubling the sample of Galactic DY
Per type stars.
