[en] We describe structural and magnetic measurements of polycrystalline, L1₀ chemically ordered Fe(55-60)Pt(45-40) films as a function of film thickness (from 3 to 13 nm) and growth temperature (270-370 deg. C). With increasing film thickness, the coercivity increases from about 1 kOe up to 11 kOe (growth at 400 deg. C), while for increasing growth temperature, the coercivity grows from 0.2 to 6 kOe for 4.3 nm thick films and 1.6 to 10 kOe for 8.5 nm thick films. There is a strong, nearly linear correlation between coercivity and the extent of L1₀ chemical order. In all the films there is a mixture of L1₀ and chemically disordered, fcc phases. The grain size in the L1₀ phase increases with both film thickness and growth temperature (increasing chemical order), while in the fcc phase the grain size remains nearly constant and is smaller than in the L1₀ phase. The films all contain twins and stacking faults. The relationship between the coercivity and the film structure is discussed and we give a possible mechanism for the lack of chemical order in the very thin films (lack of nucleation sites for the L1₀ phase)