Host-feeding patterns of Culex mosquitoes collected in southwest suburban Chicago in 2005 and 2006 were investigated using PCR and DNA sequencing techniques. We collected 1,103 bloodfed mosquitoes in 2005-2006, of which the majority (64%) were identified to be Cx. pipiens using molecular techniques. We identified the avian or mammalian host upon which the mosquito fed for 60% of the samples. Culex mosquitoes fed on 22 avian species; most common were American Robin (Turdus migratorious), Morning Dove (Zenaida macroura), House Sparrow (Passer domesticus), Blue Jay (Cyanocitta cristata), and House Finch (Carpodacus mexicanus). Additional bloodmeals were derived from 8 mammal species, primarily human and raccoon (Procyon lotor). Our study site experienced a West Nile virus (WNV) epizootic during both years, and we detected WNV in nine of the bloodfed Culex mosquitoes using quantitative PCR. The hosts of these infected bloodfed mosquitoes included three American Robins, one House Sparrow, and one human. To assess mosquito selection of hosts, we estimated the available avian host community though standardized censuses of birds from May to July. We calculated Culex feeding preferences for each bird species based on their estimated density and fraction of blood meals derived from each species. Most bird species were selected in proportion to their abundance with the exception of House Sparrows which were strongly avoided and Blue Jays which were strongly selected. These data support extensive avian and human feeding by the vector of West Nile virus, Culex pipiens, and indicate biased host selection for two abundant bird species.