 Polhill was the second son of Thomas Polhill of Otford, Kent and his wife Elizabeth Ireton, daughter of Henry Ireton, and granddaughter of Oliver Cromwell .Polhill's elder brother died, leaving him in possession of his father's inheritance.In December 1692, he was given a licence to travel to Holland which became the start of an extended Grand Tour.He visited Hanover, Brunswick, Zell, Austria, Geneva and Italy where he was at Padua University in 1694.