Kerry Feltner ; Eli Sherman kfeltner@gannett.com For 41 years, Keith MacPherson has served as a Waltham cop, rising through the ranks from patrolman to chief of the force. Last month, Chief MacPherson retired, marking the start of a new chapter for the WPD. MacPherson first assumed the role in 2012 for a year as interim chief. Two years later he was officially appointed to the position. He has served as chief for nine years. Kevin O’Connell, 27-year veteran of the department, is now the acting chief of the WPD. “It has been an honor serving under Chief MacPherson and we all wish him the very best in his retirement,” O’Connell said in a statement. “I look forward to leading the department through this transition period as we continue our work with each and every member of our community in making the City of Waltham a great place to live, work, and play.”