Northfield is a city in Atlantic County. The city has a total area of 3.5 square miles, and a population around 7,500. Northfield features Birch Grove Park, 271 wooded acres with stocked fishing lakes, over 50 campsites, trails and playground. This vast acreage combines a nature center and museum with opportunities for camping, hiking, picnicking, and nature study. Northfield also features a large bird sanctuary, dedicated to remaining open space in perpetuity.