USEF held Eventing National Championships annually at the CCI5*-L, Advanced, CCI4*-L, CCI3*-L and CCI2*-L levels. The below links provide information on each individual Championship and past results.
USEF Advanced National Championships
USEF CCI2*-L Eventing National Championships
USEF CCI3*-L Eventing National Championships
USEF CCI4*-L Eventing National Championship