An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, (7)(Lambda) He, was observed for the first time with the (e, e' K+) reaction with an energy resolution of similar to 0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The (7)(Lambda) He binding energy supplies the last missing information of the A = 7, T = 1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the Lambda N potential. DOI: 10.1103/PhysRevLett.110.012502