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We use high-quality, medium-resolution {\it Hubble Space Telescope}/CosmicOrigins Spectrograph (\HST/COS) observations of 82 UV-bright AGN at redshifts$z_{AGN}<0.85$ to construct the largest survey of the low-redshiftintergalactic medium (IGM) to date: 5343 individual extragalactic absorptionlines in HI and 25 different metal-ion species grouped into 2610 distinctredshift systems at $z_{abs}<0.75$ covering total redshift pathlengths $\Deltaz_{HI}=21.7$ and $\Delta z_{OVI}=14.5$. Our semi-automated line-finding andmeasurement technique renders the catalog as objectively-defined as possible.The cumulative column-density distribution of HI systems can be parametrized$dN(>N)/dz=C_{14}(N/10^{14} cm^{-2})^{-(\beta-1)}$, with $C_{14}=25\pm1$ and$\beta=1.65\pm0.02$. This distribution is seen to evolve both in amplitude,$C_{14}\sim(1+z)^{2.0\pm0.1}$, and slope $\beta(z)=1.73-0.26 z$ for $z<0.47$.We observe metal lines in 427 systems, and find that the fraction of IGMabsorbers detected in metals is strongly dependent on N_{HI}. The distributionof OVI absorbers appear to evolve in the same sense as the Lya forest. Wecalculate contributions to $\Omega_b$ from different components of the low-$z$IGM and determine the Lya decrement as a function of redshift. IGM absorbersare analyzed via a two-point correlation function (TPCF) in velocity space. Wefind substantial clustering of \HI\ absorbers on scales of $\Delta v=50-300$km/s with no significant clustering at $\Delta v>1000$ km/s. Splitting thesample into strong and weak absorbers, we see that most of the clusteringoccurs in strong, $N_{HI}>10^{13.5} cm^{-2}$, metal-bearing IGM systems. Thefull catalog of absorption lines and fully-reduced spectra is available viaMAST as a high-level science product at http://archive.stsci.edu/prepds/igm/.

An HST/COS Survey of the Low-Redshift IGM. I. Survey, Methodology, & Overall Results