We study, using a combination of experiment and theory, the excitation and decay of very-high-n(n∼280–430) strontium autoionizing Rydberg states formed by near-resonant driving of the 5s2S1/2→5p2P1/2 core-ion transition. The branching ratio between decay through radiative transitions and through autoionization is explored. Autoionization rates are measured as a function of both the nand ℓ quantum numbers of the Rydberg electron. The nonstationary decay dynamics is studied by creating and manipulating Rydberg wave packets and by varying the laser pulse that drives the core excitation.