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The River Ingrebourne flows north to south from its source near Brentwood to its mouth in the Rainham Marshes, where it joins the River Thames. It is 27 miles long.
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Hornchurch Country Park is on the former site of Hornchurch Airfield, in the London Borough of Havering.
The River Ingrebourne passes through the park and if forms part of Thames Chase Community Forest. The London Outer Orbital Path runs through the park. The most popular part of the park is to the west of the Ingrebourne, where the ground is flat and paved; this area is most commonly frequented by dog walkers. The woodland to the east of the river is somewhat inaccessible. Some southern parts of the park that reach into Rainham have been used as landfill.
There are a number of pillboxes and other items dating from the Second World War to be found in the park