Cooper’s grandfather, a paymaster in Henry VIII’s service, bought Pawlett manor in about 1530. The family prospered, and Cooper’s father, a soldier who sat for Whitchurch in 1584 and 1586, died in 1610 owning nearly 7,000 acres in Somerset and Hampshire, including the Rockbourne estate which he had only recently purchased. Cooper was then still a minor, but his wardship was acquired by an uncle for £324 after a sweetener of £600 was paid to lord treasurer Salisbury (Robert Cecil†).
Cooper was probably recommended to the electors of Poole in 1625 by his wife’s uncle, Sir Francis Ashley*. He is not known to have contributed to debate during the first Caroline Parliament, and was appointed only to legislative committees concerned with larceny, benefit of clergy, and concealed Crown lands (25 June). Later that year, he was assessed at £50 for a Privy Seal loan. Cooper again sat for Poole in 1628, this time failing to attract a single appointment. However, on 9 Feb. 1629 he confirmed the allegations of Catholic sympathies levelled by his friend Sir Daniel Norton* at Bishop Neile of Winchester.
Despite his hostility to popery, Cooper displayed no obvious puritan leanings, being ‘of an easy and an affable nature’ and a compulsive gambler. His first wife died of smallpox in 1628, shortly after succeeding to the Ashley estate, and Cooper, who was reputedly ‘very lovely and graceful both in face and person’, married again to another wealthy widow. According to family tradition he kept three houses fully furnished and staffed, and exercised great hospitality at each of them.
