We report a measurement of the production cross section for b hadrons in p{bar p} collisions at s = 1.96 TeV. Using a data sample derived from an integrated luminosity 83 pb¹ collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, H{sub b}, partially reconstructed in the semileptonic decay mode H{sub b} D° X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum p{sub T} > 9 GeV/c and rapidity |y| < 0.6 is = 1.30 b {+-} 0.05 b(stat) {+-} 0.14 b(syst) {+-} 0.07 b(), where the uncertainties are statistical, systematic, and from branching fractions respectively. The differential cross sections d/d{sub T}T are found to be in good agreement with recent measurements of the H{sub b} cross section and well described by fixed-order next-to-leading logarithm predictions.