We have completed a new measurement of the Stark shift in 115 In within the 410 nm 5P 1/2 → 6S 1/2 transition. We measure the Stark shift constant to be kS = −122.92(33) kHz/(kV/cm) 2 , corresponding to a difference in the 6S 1/2 and 5P 1/2 state polarizabilities, ∆α0, of 1000.2 ± 2.7 a 3 0 (in atomic units). This result is a factor of 30 more precise than previous measurements and is in excellent agreement with a new theoretical value based on an ab initio calculation of the wave functions in this three-valence-electron system. The measurement was performed in an indium atomic beam apparatus, used a GaN laser diode system, and exploited an FM spectroscopy technique to extract laser transmission spectra under conditions where our interaction region optical depth was typically less than 10 −3 .I.