One of the predictions of the ΛCDM cosmological framework is the hierarchical formation of structure, giving rise to dark matter (DM) halos and subhalos. When the latter are massive enough they retain gas (i.e., baryons) and become visible. This is the case of the dwarf satellite galaxies in the Milky Way (MW). Below a certain mass, halos may not accumulate significant amounts of baryons and remain completely dark. However, if DM particles are Weakly Interacting Massive Particles (WIMPs), we expect them to annihilate in subhalos, producing gamma rays which can be detected with the Fermi satellite. Using the three most recent point-source Fermi Large Area Telescope (LAT) catalogs (3FGL, 2FHL and 3FHL), we search for DM subhalo candidates among the unidentified sources, i.e., sources with no firm association to a known astrophysical object. We apply several selection criteria based on the expected properties of the DM-induced emission from subhalos, which allow us to significantly reduce the list of potential candidates. Then, by characterizing the minimum detection flux of the instrument and comparing our sample to predictions from the Via Lactea II (VL-II) N-body cosmological simulation, we place conservative and robust constraints on the σv − m DM parameter space. For annihilation via the τ + τ − channel, we put an upper limit of 4 × 10 −26 (5 × 10 −25 ) cm 3 s −1 for a mass of 10 (100) GeV. A critical improvement over previous treatments is the repopulation we made to include low-mass subhalos below the VL-II mass resolution. With more advanced subhalo candidate filtering the sensitivity reach of our method can potentially improve these constraints by a factor 3 (2) for τ + τ − (bb) channel.are an example of the most massive members of this population [11]. Yet, these dSphs are exceptional objects, in that they are massive enough to retain baryons (i.e., gas) and form stars. Conversely, the vast majority of the Galactic DM subhalos are not expected to host baryons and therefore remain completely dark [12]. Given their much larger number density, many of these small subhalos will be much closer to the Earth than the bigger ones, making them potentially interesting for dark matter searches.Should the Weakly Interacting Massive Particle (WIMP) DM model be correct (see, e.g., [13, 14] for a review), these objects may be detectable in the gamma-ray data. WIMPs can achieve the correct relic DM abundance (the so-called "WIMP miracle") through selfannihilation in the early Universe. Self-annihilation of WIMPs gives rise to a Standard Model (SM) particle-antiparticle pair which, among other possible subsequent by-products, typically yields gamma-ray photons. The ongoing self-annihilation of WIMPs in subhalos could be bright enough to be detectable.Since its launch in 2008, the Large Area Telescope on board the NASA Fermi Gammaray Space Telescope (Fermi-LAT) has been surveying the sky searching for gamma-ray sources [15]. The Fermi-LAT is a pair conversion telescope designed to observe the energy band from 20 MeV to gre...