Many of the farms in Sandridge appear to be very old, Heath farm was comparatively new and there are still gaps in its history. The first buildings on the site would appear to be the windmill and associated house and outhouses shown in the above map. Dury's large scale map of Hertfordshire, dated 1766, does not show the windmill and there appear to be more buildings. Research has not yet shown who lived at Windmill farm towards the end of the 18th century. However it is known that Robert Smith took the farm before 1831 (he already farmed nearby Cheapside Farm) moving into a new farm house which was completed in 1830 - as determined by the date on a roof timber. It seems that the name also changed from Windmill Farm to Heath Farm at about this date.

In 1786 the land on the east side of Sandridge Road, including several fields in St Peters parish to the south of Sandpit Lane, was farmed by John Munn and Daniel Partridge. It is seems likely that Daniel lived in Windmill Farm House and when his widow died Frederick Gough took on the "Partridge" land by 1804. Following John Munn's death, Frederick also farmed the "Munn" land from 1814. Robert Smith succeeded Frederick Gough in about 1830. During the 1860's these fields were bisected by the Midland Railway line.

In 1726 the fields between Sandridge Road and Beech Bottom were owned by Thomas Day and farmed by Thomas Kinder. They were owned by Thomas Burningham in 1843 who let them to the widow of William Brown, who lived in St Peters Street. They only became part of Heath Farm in the 1850's, while Robert Smith was still in residence. He died in 1865 and was succeeded by his son Edmund, who died in 1870.