Variational and diffusion quantum Monte Carlo (VMC and DMC) methods with Slater-Jastrow-backflow trial wave functions are used to study the spin-polarized three-dimensional uniform electron fluid. We report ground state VMC and DMC energies in the density range
0.5
≤
r
s
≤
20
. Finite-size errors are corrected using canonical-ensemble twist-averaged boundary conditions and extrapolation of the twist-averaged energy per particle calculated at three system sizes
(
N
=
113
,

259
,

and

387
)
to the thermodynamic limit of infinite system size. The DMC energies in the thermodynamic limit are used to parametrize a local spin density approximation correlation function for inhomogeneous electron systems.