  We announce the discovery of a highly inflated transiting hot Jupiter
discovered by the KELT-North survey. A global analysis including constraints
from isochrones indicates that the V = 10.8 host star (HD 343246) is a mildly
evolved, G dwarf with $T_{\rm eff} = 5754_{-55}^{+54}$ K, $\log{g} =
4.078_{-0.054}^{+0.049}$, $[Fe/H] = 0.272\pm0.038$, an inferred mass
$M_{*}=1.211_{-0.066}^{+0.078}$ M$_{\odot}$, and radius
$R_{*}=1.67_{-0.12}^{+0.14}$ R$_{\odot}$. The planetary companion has mass $M_P
= 0.867_{-0.061}^{+0.065}$ $M_{J}$, radius $R_P = 1.86_{-0.16}^{+0.18}$
$R_{J}$, surface gravity $\log{g_{P}} = 2.793_{-0.075}^{+0.072}$, and density
$\rho_P = 0.167_{-0.038}^{+0.047}$ g cm$^{-3}$. The planet is on a roughly
circular orbit with semimajor axis $a = 0.04571_{-0.00084}^{+0.00096}$ AU and
eccentricity $e = 0.035_{-0.025}^{+0.050}$. The best-fit linear ephemeris is
$T_0 = 2456883.4803 \pm 0.0007$ BJD$_{\rm TDB}$ and $P = 3.24406 \pm 0.00016$
days. This planet is one of the most inflated of all known transiting
exoplanets, making it one of the few members of a class of extremely low
density, highly-irradiated gas giants. The low stellar $\log{g}$ and large
implied radius are supported by stellar density constraints from follow-up
light curves, plus an evolutionary and space motion analysis. We also develop a
new technique to extract high precision radial velocities from noisy spectra
that reduces the observing time needed to confirm transiting planet candidates.
This planet boasts deep transits of a bright star, a large inferred atmospheric
scale height, and a high equilibrium temperature of $T_{eq}=1675^{+61}_{-55}$
K, assuming zero albedo and perfect heat redistribution, making it one of the
best targets for future atmospheric characterization studies.
