We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright (V=8.77) primary star of the HD 42176 binary system. The host is a slightly evolved late F-star likely in the very short-lived "blue-hook" stage of evolution, with \(\teff=6148\pm48{\rm K}\), \(\log{g}=4.030_{-0.026}^{+0.015}\) and \(\feh=0.034\pm0.78\). The inferred stellar mass is \(M_*=1.314_{-0.060}^{+0.063}\)\msun\ and the star has a relatively large radius of \(R_*=1.836_{-0.046}^{+0.066}\)\rsun. The planet is a typical hot Jupiter with period \(4.11379\pm0.00001\) days and a mass of \(M_P=1.524\pm0.088\)\mj\ and radius of \(R_P=1.290_{-0.050}^{+0.064}\)\rj. This is mildly inflated as compared to models of irradiated giant planets at the \(\sim\)4 Gyr age of the system. KELT-2A is the third brightest star with a transiting planet identified by ground-based transit surveys, and the ninth brightest star overall with a transiting planet. KELT-2Ab's mass and radius are unique among the subset of planets with \(V<9\) host stars, and therefore increases the diversity of bright benchmark systems. We also measure the relative motion of KELT-2A and -2B over a baseline of 38 years, robustly demonstrating for the first time that the stars are bound. This allows us to infer that KELT-2B is an early K-dwarf. We hypothesize that through the eccentric Kozai mechanism KELT-2B may have emplaced KELT-2Ab in its current orbit. This scenario is potentially testable with Rossiter-McLaughlin measurements, which should have an amplitude of \(\sim\)44 m s\(^{-1}\).