  We have derived elemental abundances of three field red horizontal branch
stars using high-resolution (R$\simeq$ 45,000), high signal-to-noise ratio (S/N
$\gtrsim$ 200) $H$ and $K$ band spectra obtained with the Immersion Grating
Infrared Spectrograph (IGRINS). We have determined the abundances of 21
elements including $\alpha$ (Mg, Si, Ca, S), odd-Z (Na, Al, P, K), Fe-group
(Sc, Ti, Cr, Co, Ni), neutron-capture (Ce, Nd, Yb), and CNO group elements. S,
P and K are determined for the first time in these stars. $H$ and $K$ band
spectra provide a substantial number of S I lines, which potentially can lead
to a more robust exploration of the role of sulfur in the cosmochemical
evolution of the Galaxy. We have also derived $^{12}$C/$^{13}$C ratios from
synthetic spectra of the first overtone (2$-$0) and (3$-$1) $^{12}$CO and
(2$-$0) $^{13}$CO lines near 23440 \AA\ and $^{13}$CO (3$-$1) lines at about
23730 \AA. Comparison of our results with the ones obtained from the optical
region suggests that the IGRINS high-resolution $H$ and $K$ band spectra offer
more internally self-consistent atomic lines of the same species for several
elements, especially the $\alpha$ elements. This in turn provides more reliable
abundances for the elements with analytical difficulties in the optical
spectral range.
