The ground-state properties of a single-component one-dimensional Coulomb gas are investigated. We use Bose-Fermi mapping for the ground-state wave function which permits solution of the Fermi sign problem in the following respects: (i) the nodal surface is known, permitting exact calculations; and (ii) evaluation of determinants is avoided, reducing the numerical complexity to that of a bosonic system and, thus, allowing simulation of a large number of fermions. Due to the mapping, the energy and local properties in one-dimensional Coulomb systems are exactly the same for Bose-Einstein and Fermi-Dirac statistics. The exact ground-state energy is calculated in homogeneous and trapped geometries using the diffusion Monte Carlo method. We show that in the low-density Wigner crystal limit an elementary low-lying excitation is a plasmon, which is to be contrasted with the high-density ideal Fermi gas/Tonks-Girardeau limit, where low-lying excitations are phonons. Exact density profiles are compared to the ones calculated within the local density approximation, which predicts a change from a semicircular to an inverted parabolic shape of the density profile as the value of the charge is increased. The recent progress in nanoscale technology has made it possible to realize clean one-dimensional quantum gases, such as ultracold atoms confined in elongated traps 1 and electrons in single-well carbon nanotubes 2 and in semiconductor quantum wires. 3 A peculiarity of a one-dimensional world is that such systems can be explained not by the conventional Landau theory of normal Fermi liquids but, rather, by an effective low-energy Luttinger liquid description, 4 generalizable to long-range Coulomb interactions. 5 A number of approaches of increasing accuracy (random-phase approximation, SingwiTosi-Land-Sjölander scheme, density functional theory) have been devised to study energetic and structural properties. 6 The most precise calculations of energy have been obtained by the Monte Carlo technique as in Ref. 7, where a quasi-onedimensional geometry with a finite width of the transverse confinement is studied. The purpose of the present work is to carry out exact calculations in a strictly one-dimensional geometry.In this paper we use the Bose-Fermi mapping to find the ground-state energy of a one-dimensional single-component Coulomb system exactly within statistical precision. The mapping applies to both homogeneous and trapped geometries.We consider a single-component system of N particles (bosons or fermions) of charge e and mass m in a onedimensional box of length L. Periodic boundary conditions are applied and the Coulomb potential is truncated for interparticle distances larger than L/2. The Hamiltonian readŝNatural length scales in a homogeneous system are defined by atomic units, that is, the Bohr radius a 0 =h 2 /me 2 for length and the Rydberg number Ry = e 2 /2a 0 for energy. The system properties are governed by a single parameter, fixed by the ratio of Bohr a 0 radius and Wigner-Seitz r s = 1/2n radius or, equiva...