The short/long-range order formation in Fe_1-x-Co_x (x < 0.3) alloys has been studied by the nuclear magnetic resonance (NMR) technique, as well as ab initio based atomistic simulation. The NMR measurements show up the formation of a certain short-range order (SRO) in dilute limit above the Curie temperature T_C and of the D0₃-type SRO (with the dominance of 3rd Co-Co nearest neighbors) in the concentration range 0.2 < x < 0.3 after quenching and subsequent annealing in the ferromagnetic state. The results of Monte Carlo simulations of binary Fe-Co alloys with ab initio interatomic interactions predict SRO in agreement with the experiment for small concentrations of Co (C_Co< 0.1), while the B2-type ordering is preferable in binary alloy in the ferromagnetic state. We demonstrate that the presence of point defects (vacancies, interstitial) can change essentially the ordering in alloys with the Co content 20-30% and result in the D0₃-type SRO formation in a reasonable agreement with the experiment.