Conduction band electrons in colloidal ZnO quantum dots have been prepared photochemically and examined by electron paramagnetic resonance spectroscopy. Nanocrystals of 4.6 nm diameter containing single S-shell conduction band electrons have g*=1.962 and a room-temperature ensemble spin-dephasing time of T2*=25  ns, as determined from linewidth analysis. Increasing the electron population leads to increased g* and decreased T2*, both associated with formation of P-shell configurations. A clear relationship between T2* and hyperfine coupling with 67Zn(I=5/2) is observed.