Lempster is a town in Sullivan County, New Hampshire, United States. The population was 1,118 at the 2020 census. Settlements include the town center and the village of East Lempster. First granted by colonial governor Jonathan Belcher in 1735 as "Number 9", it was regranted in 1753 as "Dupplin", after Scottish lord Thomas Hay, Viscount Dupplin…Lempster is a town in Sullivan County, New Hampshire, United States. The population was 1,118 at the 2020 census. Settlements include the town center and the village of East Lempster. First granted by colonial governor Jonathan Belcher in 1735 as "Number 9", it was regranted in 1753 as "Dupplin", after Scottish lord Thomas Hay, Viscount Dupplin, by Governor Benning Wentworth. The town was re-granted one final time in 1767 as Lempster, after Sir Thomas Fermor, Second Baron Leominster or "Lempster", and incorporated in 1772.