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Recent discoveries of intrinsic 2D ferromagnetism in van der Waals materials provide promising platforms for studying fundamental ferromagnetism in atomically thin limit. Most of these materials are found to be insulators/semiconductors and extremely sensitive to air. Here, we show that Fe₃GeTe₂ is a ferromagnetic metal down to monolayer limit with strong perpendicular anisotropy. Using both magneto-optical spectroscopy and electrical transport measurements, we establish the cross over from 3D to 2D Ising ferromagnetism as a function of layer thickness, which accompanies the fast drop of Curie temperature.