This article presents a new method for the placement of distribution-level phasor measurement units (D-PMUs) in the active distribution networks (ADNs). The new objective function and constraints are proposed to ensure the minimization of capital cost as well the maximization of system observability, in the presence of distributed generations (DGs), zero injection buses (ZIBs), and tie-switches. The integer linear programming (ILP) is used to solve the framed objective function and the constraints. Furthermore, the accuracy of ADN state estimation (ADN-SE), in various system conditions, such as network reconfiguration, change in load demand, and measurement error degradation, is analyzed to check the impact of the proposed placement. The uncertainties caused by D-PMUs, DGs, and pseudomeasurements are considered well in ADN-SE using Monte Carlo simulations. The IEEE 69, 123, Indian 85, and UKGDS 95 bus distribution systems are used in the case studies.