An extensive analysis of the origins of William Knopp of Watertown was published by Clifford L. Stott in 1993.
Stott's analysis of the various parish, land and probate records distinguishes the various William Knopps of the region, and concludes that William Knopp of Watertown, MA was the son of Thomas Knopp and Alice Howlat. This article is a must-read for descendants of William Knopp.
William was indentured to Sir Richard Saltonstall when he arrived in America in 1630 - probably for the amount of passage for himself and his family. Sir Richard sailed with the Winthrop Fleet. Other passengers were also from Suffolk.
30 Nov 1630, the Court of Assistants in Watertown ordered that whoever employed Willm Knopp or his son in any work was to pay half their wages to Sr. Rich. Siltonstall & whoever buys boards from them to pay one half the price to Sr. Richard, until the money disbursed for them be satisfied.
William was eventually granted seven parcels of land in Watertown, a 16 acre homestall, a 93 acre farm, 30 ares in the Great Divident, and smaller parcels which totalled another 29 acres. As an old man, he performed work around the meeting house and was the poundkeeper - he was referred to as "Ould Knop" or "Father Knop".
In 1656, William applied for assistance to the selectmen of Watertown who proposed he place his estate in the hands of his children in exchange for their support, but the children refused to do so. During the last years of his life, the town leased out William's lands and reimbursed others for their assistance to him.
William Knopp died in Watertown, MA 30 Aug 1659 [sic, recte 1658] "aged about 80 years."
His will dated 5 Jul 1655 was never proved, possibly because of ambiguous language. Daughter Anne had died but the will not modified to dispose of her portion. Elizabeth Buttery of Bures St. Mary was the daughter still in England - she appointed attorneys to receive her portion but she died before she received her share. The heirs in New England indicated in a deed dated 1 Apr 1662, that their father had died intestate. The estate inventory was taken 31 Aug 1658.
His widow died by 1 Apr 1662 when the heirs sold the real estate that they had inherited, apparently including the widow's thirds. 
By first wife:
Elizabeth Knopp, baptized 10 July 1608, at Wormingford. Married Mr. Buttery. Did not emigrate.
William Knopp, baptized 3 February 1610/1, at Wormingford. Immigrated to Watertown, Massachusetts. Married (1) Mary by 1642 and (2) Margaret by 1652.
Mary Knopp, baptized 19 August 1613, Wormingford. Married by 1637 Thomas Smith of Watertown.
Ann Knopp (also spelled Anne or Anna), baptized 24 December 1618 in Wormingford; married John Philbrick in New England.
John Knopp, baptized 20 January 1622/3 at Bures St. Mary, Sussex; married Sarah Young in Watertown.
James Knopp, baptized 30 April 1626 at Wormingford; married Elizabeth Warren, daughter of John Warren, in Watertown.
Judith Knopp, baptized 16 July 1629, Bures St. Mary; married Nicholas Cady in Watertown.
Judith was married to William Knopp on 11 Jan 1606/7 in Wormingford, Essex, England. She was the mother of his children:
William Knopp appeared many times in Watertown records:
p.24 8 Oct 1651 reference to ?ould Knop? - received payment from the town
p.25 10 Dec 1650 [should have been 1651 according to surrounding entries] disbursements by John Shearman to ?ould Knop? for wages
p.28 Jan 12 1651 Ordered that ould father Knop shall be payd out of this p'sent rate whatsoever he can make appeere to be due to him and to be Discharged of his service aboute the meeting house and keep of the pound when his yeare is expired which will be upon the first of May in '52.
p.30 Feb 3, 1651 Ordered that Sergent Beeres shall view the severall pertickerlers of old Knops work done at the meeting house and to make a returne to the towne
p.55 15 Dec 1657 10# for ould Knop ?credit given to the town all wch somes are to be pd in this 50L rate wth the severall debts dew to the towne
p.56: Jan 29 1657 By Left. Beeres there is pd in the behalfe of the towne as lent to Willi Knop the Elder the some of fower poundes, eighteene shillings & eleaven pence. Other sums: By Michaell Bearsto for Ould knop;More by Mich: Bearsto.
p.56 Thomas Hastings howse Apr 13, 1658. The Land of Ould Knop his meadow & corne land is lett to Robt Jenison & Sargt Bloyse for this yeare att the rate of five pounds & if in case it continew in the hands of the select men to lett it, they do ingage the above named have it all the time that it continew in the same hands to lett
Lands & Proprietors?
25 Jul 1636 Grant of great dividents lotted out by the Freemen to all the Townsmen being 120 in number. 4 Division, each 160 rods in breadth.
First Division - Lott 23, William Knop, 30a
2nd Division - Lott 17, Nicholas Knap 30a
First Inventory of Grants and Possessions - William Knop Sen.:
An homestall of 16a bounded SE & SW with Robert Lockwood & Nicholas Knap, the E with Richard Browne, NE with Richard Beers, N with the highway & the W with George Munnings
7a of Plowland in the further Plaine & the 86 Lott
8a of Plowland in the further Plaine & the 52 Lott
7a of Meddow in the remote Meddowes & the 99 Lott
7a & halfe of upland beyind the further Plaine & the 31 Lott
30a of upland being a great Divident in the 1st Division & 23 Lott
A farme of 93 acres of upland in the 1st Division
Grants & Possessions of the Lands in Watertown: According to order of the Court of 9 (7) 1639; Attested Feb 27 1714/15
William Knop, Sen
Missing the 8 acres of plowland in the first inventory
Missing the farm
Added: One acre of Meaddow by estimation in West meddow bounded wth common land granted to him
↑ 1.01.1 Stott, Clifford, L., (1993) "English Origins of William and Judith (Tue) Knopp of Watertown, Massachusetts." New England Historical and Genealogical Record, Vol. 147. AmericanAncestors.org (Vol 147, Pages 315-328).
↑ 2.02.12.2 Robert Charles Anderson, (1995) "William Knopp," Featured name, The Great Migration Begins ..., Volumes I-III. NEHGS AmericanAncestors.org (Volumes I-III, Pages 1143-46) which frequently cites Stott (1993).
↑ Stott, Clifford, L., (1993) "English Origins of William and Judith (Tue) Knopp of Watertown, Massachusetts." New England Historical and Genealogical Record, vol. 147 ( page 323.
↑ 6.06.1 Historical Society of Watertown, (1894) Watertown Records Comprising the First and Second Books ... Watertown, MA: Fred G. Baker Pr., Archive.org (Town Procedings, Pages 24-56; Supplement: Births, Deaths & Marriages, Page 21).
Since it has been fairly well proved that William Knopp was a son of Thomas Knopp and Alice Howlat - why have these erroneous parents and siblings never been removed?
Children baptized at Bures St. Mary, that are apparently the children of Thomas & Alice were:
Elizabeth Knopp, bp. 9 Mar 1571/2
James, bp 19 Sep 1574
John, bp 13 Jul 1578
William, bp 1 Jan 1580/1
Thomas, bp 15 Mar 1583/4 as "the sonne of Thomas"
Margaret, bp 7 Nov 1586 "daughter of Thomas"
Ann, bp 13 Jan 1590/1 "daughter of Thomas"
Robert, bp 3 Feb 1593/4 "sonne of Thomas"