Neutrino Elastic scattering Observation with NaI (NEON) is an experiment designed to detect neutrino-nucleus coherent scattering using reactor electron antineutrinos. NEON is based on an array of six NaI(Tl) crystals with a total mass of 13.3 kg, located at the tendon gallery that is 24 m away from a reactor core with a thermal power of 2.8 GW in the Hanbit nuclear power complex. The installation of the NEON detector was completed in December 2020, and since May 2021, the detector has been acquiring data at full reactor power. This paper describes the design of the NEON detector, including the shielding arrangement, configuration of the NaI(Tl) crystals, and associated operation systems. The initial performance and associated sensitivity of the experiment are presented.