We report the evolution of magnetic moment as well as magnetic anisotropy with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed laser deposition. The films become more ordered as the annealing temperature ($T_A$) increases from 400 to 600 $^0$C. The extent of emph{L}$2_1$ ordering in the films annealed at 600 $^0$C is $approx 96%$. The static magnetization measurements by vibrating sample magnetometry shows a maximum moment of 4.95 $mu_B$ per formula unit with low coercivity ($H_C$ $approx$ 65 Oe) in the films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar angle dependent ferromagnetic resonance (FMR) measured at several temperatures allows determination of various anisotropy fields relevant to our system as a function of $T_A$. Finally, we have evaluated the exchange stiffness constant down to 100 K using spin wave modes in FMR spectra. We have also estimated the exchange energies as well as stiffness constant by varying the lattice parameter emph{ab-initio} using the Korringa-Kohn-Rostoker method.
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