The ground state properties of (31)Mg indicate a change of nuclear shape at N = 19 with a deformed J(pi) = 1/2(+) intruder state as a ground state, implying that (31)Mg is part of the ``island of inversion''. The collective properties of excited states were the subject of a Coulomb excitation experiment at REX-ISOLDE, CERN, employing a radioactive (31)Mg beam. De-excitation gamma-rays were detected by the MINIBALL gamma-spectrometer in coincidence with scattered particles in a segmented Si-detector. The level scheme of (3I)Mg was extended. Spin and parity assignment of the 945 keV state yielded 5/2(+) and its de-excitation is dominated by a strong collective M1 transition. Comparison of the transition probabilities of (30,31,32)Mg establishes that for the N = 19 magnesium isotope not only the ground state but also excited states are largely dominated by a deformed pf intruder configuration. (C) 2011 Elsevier B.V. All rights reserved.