Single layers of graphene (SLG) mechanically exfoliated from highly oriented pyrolytic graphite and deposited on SiO2/Si were irradiated with C+ ions at different fluences (from 1013 to 1014 cm-2), in order to modify the transport properties in controlled way. Using a method based on scanning probe microscopy, local measurements of the electron mean free path (l) have been carried out both on pristine and ion irradiated SLG. A lateral inhomogeneity of l was found in both cases, with an increasing spread in the distribution of l for larger fluences. Before irradiation, the spread was explained by the inhomogeneous distribution of charged impurities on SLG surface and/or at the interface with SiO2. After irradiation, lattice vacancies cause a local reduction of l in the damaged regions.