We present a unique approach to demonstrating probabilistic bits (p-bit) leveraging perimeter-gated single-photon avalanche diodes (pg-SPADs). By exploiting the pg-SPAD’s dark count rate (DCR) modulation property, we show a compact circuit design approach for probabilistic computing. Measured results from an array of pg-SPAD-based p-bits fabricated in 0.35 μm CMOS validate the tunable random number generation capability of these devices. In addition, experimentally calibrated circuit simulations—based on measured device data—confirm that these pg-SPAD-based p-bits can scale efficiently to form large probabilistic circuits (p-circuits). This work highlights a viable route toward building CMOS-compatible p-circuits for resource-constrained and large-scale applications alike.