Chelmsford has been the county town of Essex for many centuries, lying roughly at its centre. The Rivers Can and Chelmer join in the east of the town then flow east to the Blackwater Estuary. Hanningfield Reservoir lies a few miles to the south.

Its largest single wildlife site is Hylands Park, an historic park south-west of the town. There are a few small sites in the valley of the Chelmer and a cluster around the reservoir, while Danbury to the east is ringed by valuable sites, much of it former common land. South of Chelmsford there is another well-preserved ancient common at Galleywood, and a couple of small ancient woods.

Brentwood to the south-east has two large historic parkland sites close by – Thorndon (with some recent additions) and Weald. North of Brentwood is what remains of Writtle Forest, privately owned but with some public access, and still with the feel of a medieval forest.

Billericay has Norsey Wood, probably the finest ancient wood in the area, and some equally fine wildflower meadows.