We present an analysis of the galaxy distribution surrounding 15 of the most luminous ( \gtrsim 10 ^ { 14 } L _ { \odot } ; { M _ { 1450 } } \simeq - 30 ) QSOs in the sky with z \simeq 2.7 . Our data are drawn from the Keck Baryonic Structure Survey ( KBSS ) , which has been optimized to examine the small-scale interplay between galaxies and the intergalactic medium ( IGM ) during the peak of the galaxy formation era at z \sim 2 - 3 . In this work , we use the positions and spectroscopic redshifts of 1558 galaxies that lie within \sim 3 ^ { \prime } ( 4.2 h ^ { -1 } comoving Mpc ; cMpc ) of the hyperluminous QSO ( HLQSO ) sightline in one of 15 independent survey fields , together with new measurements of the HLQSO systemic redshifts . By combining the spatial and redshift distributions , we measure the galaxy-HLQSO cross-correlation function , the galaxy-galaxy autocorrelation function , and the characteristic scale of galaxy overdensities surrounding the sites of exceedingly rare , extremely rapid , black hole accretion . On average , the HLQSOs lie within significant galaxy overdensities , characterized by a velocity dispersion \sigma _ { v } \simeq 200 km s ^ { -1 } and a transverse angular scale of \sim 25 ^ { \prime \prime } ( \sim 200 physical kpc ) . We argue that such scales are expected for small groups with log ( M _ { \textrm { \scriptsize { h } } } /M _ { \odot } ) \simeq 13 . The galaxy-HLQSO cross-correlation function has a best-fit correlation length r _ { 0 } ^ { \textrm { \scriptsize { GQ } } } = ( 7.3 \pm 1.3 ) h ^ { -1 } cMpc , while the galaxy autocorrelation measured from the spectroscopic galaxy sample in the same fields has r _ { 0 } ^ { \textrm { \scriptsize { GG } } } = ( 6.0 \pm 0.5 ) h ^ { -1 } cMpc . Based on a comparison with simulations evaluated at z \sim 2.6 , these values imply that a typical galaxy lives in a host halo with log ( M _ { \textrm { \scriptsize { h } } } /M _ { \odot } ) = 11.9 \pm 0.1 , while HLQSOs inhabit host halos of log ( M _ { \textrm { \scriptsize { h } } } /M _ { \odot } ) = 12.3 \pm 0.5 . In spite of the extremely large black hole masses implied by their observed luminosities [ log ( M _ { \textrm { \scriptsize { BH } } } /M _ { \odot } ) \gtrsim 9.7 ] , it appears that HLQSOs do not require environments very different from their much less luminous QSO counterparts . Evidently , the exceedingly low space density of HLQSOs ( \lesssim 10 ^ { -9 } cMpc ^ { -3 } ) results from a one-in-a-million event on scales < < 1 Mpc , and not from being hosted by rare dark matter halos .