Situated in central Essex, a few miles north-west of Chelmsford, medieval Pleshey acquired the form of a castle-town, largely encircled by an enclosed deer park – the Norman-French place-name referring to a hedge around a partly forested area – with residents' field strips along the western side of the village. There are modest traces of older settlement on the site, but not Saxon, and Domesday Book has no reference to Pleshey per se. The castle – steep motte with a northern bailey – had been put up at the edge of Mandeville land in High Easter parish by mid-twelfth century, likely by Geoffrey II de Mandeville, Earl of Essex, then refortified and enlarged in phases, with royal licence (ca. 1166-80), by the third earl, William de Mandeville, for whom it served as administrative centre of his regional estates. It is uncertain which phase saw the construction of a semi-circular southern bailey – perhaps superseding the northern bailey thought destroyed 1157/58 after the strongholds of the rebellious de Mandevilles were ordered to be slighted – as a settlement enclosure, and the erection of a church in the north-west quadrant of the enclosure to serve the castle and village communities, as a chapel (dedicated 1175) of the High Easter parish church; this chapel is assumed to have been replaced by a full church in mid-thirteenth century.

The settlement appears the product of some planning, laid out along an east-west main street, still known simply as The Street, a back lane formed when the northern bailey ditch was infilled, (but lacking evidence of residences on its outer side), and a street – known as New Street in the thirteenth century – connecting the back lane and the northern entrance through the enclosure. This settlement does not show signs of having expanded beyond the centre to fill the enclosure (roughly 14 hectares). Pleshey later passed, along with the earldom, through marriage, to the de Bohun family (1227/28), which situated the court of the honour at High Easter manor, and in the fifteenth century was used as part of the dowry for English queens. High Easter manor is not known to have had its own market. Modifications in 1393/94 introduced a new church, just outside the enclosure – indicative of the reduced military value of the defences – served by a college of canons, and superseding the older church. In the sixteenth century abandonment and dereliction of the castle deprived the settlement of a key consumer of goods and services, while the Reformation put an end to the college of canons; Pleshey gradually reverted to an agricultural community, reflected in a significant reduction of pottery finds. However, the marketplace – thought positioned, as a semi-circular expansion within a middle section of The Street, echoing the curve of the bailey and with a small number of plots laid out between the marketplace and back lane – was not fully infilled and out of operation until the eighteenth century.

The introduction, or redevelopment, of planned settlement within Pleshey castle's southern bailey seems have been associated with the institution of a market-town, unchartered as far as we know, presumably another expression of a policy already successfully effected at Saffron Walden by Geoffrey de Mandeville. The earliest reference encountered to a market is in a document datable to before 1274, though the owner is not identified [R.H. Britnell, "Essex Markets Before 1350," Essex Archaeology and History, vol.13 (1981), p.16]. The inquisition post mortem on Earl John de Bohun in 1336 shows him holding a Saturday market there and a fair at a late June festival unassociated with the church dedication, although part of that dedication was to St. Nicholas, appropriate for a market settlement church, and conceivably the dedication of the older de Mandeville chapel; market stalls and burgess tenants are mentioned. The manorial court rolls, surviving from the opening years of Edward I's reign, make reference to a Pleshy Burgus, though this does not seem to refer to more than the implementation of burgage tenure within at least parts of Pleshey; the number of landless messuages subject to real estate transactions at Pleshey supports the notion of an introduced burghal component facing at least one side of the marketplace, though none of these transactions occurs before mid-fourteenth century and none clearly shows any shop involved. A rental of 1273/74, however, identified 46 shops, 9 stalls, and 3 workshops, though these were at various locations, not just the marketplace. Some of these were still operating in the post-medieval period.

That no licence is known for market or fair suggests neither was expected to generate substantial or growing profits for the owner. Pleshey was not located on any major road or river route and does not look like an effort to capture any particular share of itinerant commerce; it was rather the Mandeville transfer of principal residence from Saffron Walden to Pleshey that warranted establishing a market settlement by the castle, which was in a location that lacked any notable geographical advantage as regards commercial routes [M.R. Petchey, "The archaeology of medieval Essex towns," in Archaeology in Essex to AD 1500, Council for British Archaeology Research Report no.34 (1980) p.116]. Already, by the time a market settlement was in place at Pleshey, it was ringed by markets under other ownership within a day's journey, notably Chelmsford, Harlow, Hatfield Broad Oak, Witham, and Great Dunmow, and these at-hand rivals would later be augmented by Chipping Ongar, Writtle and Braintree. But none belonged to the earls of Essex except (intermittently) that at Hatfield, held on the same day as Pleshey's. The 5th earl, Humphrey de Bohun, acquired (1318) a licence for market and fair at the Essex manor of Fobbing, but was not the original licensee; he also licensed such institutions at Enfield (Middx., 1303) and Pinchbeck (Lincs., 1318), but was not prolific as a market-founder; his like-named successor, a nephew, died (1373) in possession of a number of manors in Essex or neighbouring counties known to have had markets, but some (e.g. Great Baddow, Great Wakering, Ramsden Bellhouse) were not foundations of the Bohun or Mandeville earls, and several others were marketless. Whether Humphrey's complaint in 1341 that a group of men from Thaxted, Writtle, Chipping Ongar and elsewhere broke into, and hunted in, his deer parks at Pleshey and other of his manors, reflects, at least in part, any trade rivalry, is not evident.

On the other hand, if Pleshey's market was established primarily to service the earl's castle and settlement, as would seem probable, particularly given that the market street was laid out to cross the bailey right in front of the castle, medieval pottery finds on the castle site – some local coarse ware, manufactures from elsewhere in East Anglia, and a little (later examples) imported from abroad – have not yet been echoed by similar finds within the town and so do not point to the imported wares, at least, being purchased through local commercial institutions.

There is no indication that any particular industry was well-established in medieval Pleshey; certainly the cloth industry and trade are not well-evidenced, no retailer of cloth products being documented before 1471. A family of smiths is seen during the reign of Edward II, and two dyers and a rope-maker in conjunction with landless messuage transactions in mid-fourteenth century, but none of this extends beyond the potential needs of the local community. The same might be said of other artisans or tradesmen, who seem to have been associated with victualling and building trades. Pleshey's characteristics barely qualify it for categorization as urban, and it is only its role as a seigneurial base that seems to warrant describing it as a market town.