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The effect of doping and microstructure is explored on CVD diamond MEMS resonators. Hundreds of surface micromachined double ended tuning fork (DETF) resonators were fabricated in nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) films deposited using hot filament CVD technique with varying levels of Boron doping. High resistivity (1926 MΩ·cm) NCD cantilevers and DETF demonstrated impressive Q-factors of 232,562 at f = 61.86 kHz and Q = 201,435 at f = 263.66 kHz, respectively. These Q's are the highest Q-factors yet reported for diamond resonators and the highest for cantilevers fabricated from any polycrystalline material. Higher boron doping resulted in reduced Q due to defect losses. Higher surface loss was observed in both MCD and NCD as doping increased. Observed Q-factors were almost the same for MCD and NCD at frequencies near 10 MHz.