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
r
s
. 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
=
2
k
F
grows as the wire width decreases. We obtain the Tomonaga-Luttinger liquid parameter
K
ρ
from the momentum density. It is found that
K
ρ
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
≪
r
s
<
1
. It is found that the correlation energy varies as
b
2
for
b
≪
r
s
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
r
s
≤
1
. These are compared with the QMC results in the range of applicability of the theory.