Measurements of the susceptibility between 1.25 and 300 K and of the magnetization from 0 to 50 kG are reported for a series of boron-doped silicon samples spanning the metal-nonmetal transition. As for Si:P, the magnetic properties change gradually in this field and temperature range as the boron concentration is varied across the transition. The susceptibility consists of (at least) two contributions: a component associated with the randomly distributed localized holes interacting via short-range antiferromagnetic exchange, and a component which maps the evolution of extended holes from a degenerate to a nondegenerate gas. The latter is a positive term which decreases in magnitude as the number of delocalized holes increases with increasing boron concentration. The impurity magnetization is not saturated at 1.25 K and 50 kG, and is small compared to the magnetization of an equivalent number of uncoupled boron impurities. Results for both the susceptibility and magnetization indicate that exchange plays a more important role in Si:B than it does in Si:P.