Hunterdon County — where residents have a median household income of $106,143 — is the wealthiest county in New Jersey and also the healthiest for the sixth straight year, according to this year’s annual analysis co-sponsored by the Robert Wood Johnson Foundation and the University of Wisconsin Population Health Institute. Meanwhile, Cumberland County — with a median household income of $50,750 and a poverty rate of 18 percent — is the poorest and least healthy in the state.