LHS 1678 is a cool M-dwarf (about 0.34 solar masses, 3,490 K, 0.33 solar radii), 19.9 light-years from Earth. LHS 1678 b is a planet with 0.7 Earth radii, with an orbital period of 20.6 hours, at 0.012 AU from its star, discovered in 2021 via transit. LHS 1678 c is a planet with 0.9 Earth radii, with an orbital period of 3.7 days, at 0.033 AU from its star, discovered in 2021 via transit. LHS 1678 d is a planet with 1.0 Earth radii, with an orbital period of 5.0 days, at 0.040 AU from its star, discovered in 2024 via transit.