Motivated by intriguing properties of geometrically frustrated systems, in the present work, new member of the triple perovskite family, Ca3CoSb2O9, with a Co2+ triangular motif, has been synthesized, and its structural, magnetic, and thermal transport properties were studied in detail. The 6H-perovskite crystallizes in the monoclinic phase with a P 21/c1 symmetry. A cusp in the dc magnetic susceptibility, accompanied by a λ-like feature in the ac susceptibility and specific heat, indicates a transition to an antiferromagnetic state below TN ∼ 3.8 K. Magnetic susceptibility measurements confirm the existence of the Co2+ moments with S = 1/2 spin state, a large Curie-Weiss temperature of θCW = −76.70 K, and a significant degree of magnetic frustration (f = |θCW/TN| ≈ 20). The temperature-dependent ac magnetization reveal a prominent peak at TN that exhibits characteristic magnitude suppression and a subtle shift (3.8 to 4.1 K) with increasing frequency from 0.21 to 631 Hz. Additionally, a nondispersive kink at T ∼ 7.0 K was observed, indicative of persistent short-range magnetic correlation above TN. Moreover, the absence of a spin-flop transition or a Ms/3 magnetization plateau in field-dependent studies up to 16T, suggests that the structural distortions in Ca3CoSb2O9 stabilize a non-collinear 120° spin structure against field-induced quantum phase transitions.