We report precise radial velocity (RV) measurements of WASP-47, a G star that hosts three transiting planets in close proximity (a hot Jupiter, a super-Earth and a Neptune-sized planet) and a non-transiting planet at 1.4 AU. Through a joint analysis of previously published RVs and our own Keck-HIRES RVs, we significantly improve the planet mass and bulk density measurements. For the super-Earth WASP-47e ($P$ = 0.79 days), we measure a mass of 9.11 $pm$ 1.17 $M_oplus$, and a bulk density of 7.63 $pm$ 1.90 g cm$^{-3}$, consistent with a rocky composition. For the hot Jupiter WASP-47b ($P$ = 4.2 days), we measure a mass of 356 $pm$ 12 $M_oplus$ (1.12 $pm$ 0.04 $M_rm{Jup}$) and constrain its eccentricity to $<0.021$ at 3-$sigma$ confidence. For the Neptune-size planet WASP-47d ($P$ = 9.0 days), we measure a mass of 12.75 $pm$ 2.70 $M_oplus$, and a bulk density of 1.36 $pm$ 0.42 g cm$^{-3}$, suggesting it has a thick H/He envelope. For the outer non-transiting planet, we measure a minimum mass of 411 $pm$ 18 $M_oplus$ (1.29 $pm$ 0.06 $M_rm{Jup}$), an orbital period of 595.7 $pm$ 5.0 days, and an orbital eccentricity of 0.27 $pm$ 0.04. Our new measurements are consistent with but 2$-$4$times$ more precise than previous mass measurements.
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