Mountnessing is a village in the Borough of Brentwood in south Essex, England. It is situated to the north-east of Brentwood, south-west of Ingatestone. A large proportion of the houses are situated on the Roman Road (formerly the A12 road until the village was bypassed in the 1970s) between Brentwood and Ingatestone. The village is approximately equidistant between the two closest railway stations of Shenfield and Ingatestone. There is a primary school, Mountnessing C of E, on Roman Road. St.Giles church is located midway between Mountnessing and Billericay.