We study the ground-state properties of ferromagnetic quasi-one-dimensional quantum wires using the quantum Monte Carlo (QMC) method for various wire widths b and density parameters rs. The correlation energy, pair-correlation function, static structure factor, and momentum density are calculated at high density. It is observed that the peak in the static structure factor at k=2kF grows as the wire width decreases. We obtain the Tomonaga-Luttinger liquid parameter Kρ from the momentum density. It is found that Kρ increases by about 10% between wire widths b=0.01 and b=0.5. We also obtain ground-state properties of finite-thickness wires theoretically using the first-order random phase approximation (RPA) with exchange and self-energy contributions, which is exact in the high-density limit. Analytical expressions for the static structure factor and correlation energy are derived for b≪rs<1. It is found that the correlation energy varies as b2 for b≪rs from its value for an infinitely thin wire. It is observed that the correlation energy depends significantly on the wire model used (harmonic versus cylindrical confinement). The first-order RPA expressions for the structure factor, pair-correlation function, and correlation energy are numerically evaluated for several values of b and rs≤1. These are compared with the QMC results in the range of applicability of the theory.