Supermassive black hole (SMBH) mass estimates are derived for 1743 galaxies from the Millennium Galaxy Catalogue (MGC) using the recently revised empirical relation between SMBH mass and the luminosity of the host spheroid. The MGC spheroid luminosities are based on R1/n bulge plus exponential-disc decompositions. The majority of black hole masses reside between 106 M⊙ and an upper limit of 2 × 109 M⊙ . Using previously determined space-density weights, we derive the SMBH mass function which we fit with a Schechter-like function. Integrating the black hole mass function over 106 < Mbh/M⊙ < 1010 gives an SMBH mass density of ( 3.8 ± 0.6) × 105 h370 M⊙ Mpc−3 for early-type galaxies and ( 0.96 ± 0.2) × 105 h370 M⊙ Mpc−3 for late-type galaxies. The errors are estimated from Monte Carlo simulations which include the uncertainties in the Mbh–L relation, the luminosity of the host spheroid and the intrinsic scatter of the Mbh–L relation. Assuming SMBHs form via baryonic accretion, we find that ( 0.008 ± 0.002) h370 per cent of the Universe's baryons are currently locked up in SMBHs. This result is consistent with our previous estimate based on the Mbh–n (Sérsic index) relation.