The cross section for jets from b quarks produced with a W boson has been measured in pp collision data from 1.9  fb−1 of integrated luminosity recorded by the CDF II detector at the Tevatron. The W+b-jets process poses a significant background in measurements of top quark production and prominent searches for the Higgs boson. We measure a b-jet cross section of 2.74±0.27(stat)±0.42(syst)  pb in association with a single flavor of leptonic W boson decay over a limited kinematic phase space. This measured result cannot be accommodated in several available theoretical predictions.