We study dark photon dark matter X associated with a dark U(1)X gauge symmetry. To evade laboratory and cosmological constraints on kinetic mixing with the Standard Model U(1)Y, we assign a Z_2-odd dark parity to X that forbids such mixing. The leading interactions then arise from gauge-invariant dimension-6 Higgs-portal operators, including both parity-even and parity-odd terms. We assume that the dark matter mass is generated via the Stueckelberg mechanism. In the interacting Stueckelberg EFT, a gauge-invariant dimension-6 parent reduces in unitary gauge to the nominal dimension-4 Higgs-portal interaction (H^H)X_X, with its coefficient correlated with m_X^2/2, while additional derivative operators are organized by the same longitudinal-mode power counting. We investigate freeze-in production of X from Higgs-pair annihilations after reheating, incorporating both field-strength and Stueckelberg-allowed operators. First, we consider the case in which the Wilson coefficients of the gauge-invariant dimension-6 operators, C and , are of order unity. Under a conservative single-cutoff power counting in which the strong-coupling scales of the longitudinal mode lie above the cutoff of the field-strength effective theory, we find that the Stueckelberg contributions remain subdominant in dark matter production. We emphasize that this ordering of scales is an explicit assumption rather than a universal consequence of perturbative unitarity. Next, we explore a more general situation in which C and are smaller than unity. In this second case, Stueckelberg-allowed operators can become comparable and generate contributions proportional to T{}^3, T{}^5, and T_{}^7, including sign-dependent interference effects. For both cases, we show that there exists a wide parameter space consistent with the observed dark matter relic density.