  We present an unbiased census of starless cores in Perseus, Serpens, and
Ophiuchus, assembled by comparing large-scale Bolocam 1.1 mm continuum emission
maps with Spitzer c2d surveys. We use the c2d catalogs to separate 108 starless
from 92 protostellar cores in the 1.1 mm core samples from Enoch et al. (2006),
Young et al. (2006), and Enoch et al. (2007). A comparison of these populations
reveals the initial conditions of the starless cores. Starless cores in Perseus
have similar masses but larger sizes and lower densities on average than
protostellar cores, with sizes that suggest density profiles substantially
flatter than r^-2. By contrast, starless cores in Serpens are compact and have
lower masses than protostellar cores; future star formation will likely result
in lower mass objects than the currently forming protostars. Comparison to
dynamical masses estimated from the NH_3 survey of Perseus cores by Rosolowsky
et al. (2007) suggests that most of the starless cores are likely to be
gravitationally bound, and thus prestellar. The combined prestellar core mass
distribution includes 108 cores and has a slope of -2.3+/-0.4 for M>0.8 Msun.
This slope is consistent with recent measurements of the stellar initial mass
function, providing further evidence that stellar masses are directly linked to
the core formation process. We place a lower limit on the core-to-star
efficiency of 25%. There are approximately equal numbers of prestellar and
protostellar cores in each cloud, thus the dense prestellar core lifetime must
be similar to the lifetime of embedded protostars, or 4.5x10^5 years, with a
total uncertainty of a factor of two. Such a short lifetime suggests a dynamic,
rather than quasi-static, core evolution scenario, at least at the relatively
high mean densities (n>2x10^4 cm^-3) to which we are sensitive.
