A list of early residents in Octoraro Hundred is given at MySource:Petition, Octoraro Hundred, Cecil County, MD, 1766. The list is dominated by Porters, Ewings, and Gillespie's, all belived to be members of a single, large, extended family.
Nathaniel Porter From Egle, 1894
(pages in Egle, 1894 containing references to "Porter" 60 84 107 163 164 186 192 196 227 262 272 313 352 394 446 518 557 649 )
November 8th, 1751. William Wyerman enters a Caveat against a Survey or the Return of a Survey made by Mr. Stevenson for Nathaniel Porter, on a Tract of Land including John Portmans Improvement in Reading Township, York County, which said Wyerman obtained a Warrant for e 21st June, 1748. for RICHARD PETERS, Sec'ry
Ben Porter from Ben Porter, personal Communication, 29 May 2009 User:Ben Porter
I've been actively on the search for Patrick's siblings and ancestors.
I've found but not yet synthesized 82 property records from Cecil County in the period ca 1675 to ca 1810 that involve the Porters. A noticeable number of these involve Ewings (James, Patrick, Nathan) and Gillespies (James, though other Gillespie's appear in this part of the index just not on transactions with Porters). The two Porter forenames that I scan for are Patrick (no results) and Samuel (possibly his father's name, but no results). Other Porter forenames appearing in the records are quite common ones that frequently occurred in my family for the generations following Patrick (e.g., John, James, Benjamin, Elizabeth, Mary, Margaret) but because these are fairly common I have no idea if there is a true connection. There are some other forenames (Robert, Stephen) in the property records that do not appear in my family line. So, nothing definitive yet but I am really just getting underway.
I am curious about the Delaware miller you mentioned that had a son named Patrick who has not been traced. Can you provide any dates? What was this Porter's name? FYI, there was a Stephen Porter who owned and operated a mill on Octoraro Creek in Cecil County, at about the same time that Patrick was operating his mill in what is now Scott County, VA. I don't know how common this skill set was among early settlers, but I figure one must know a thing or two to construct a dam, mill pond, and the mill itself, so maybe some connection will be revealed as this is further explored.
Currently, I am awaiting a copy of a will of a Samuel Porter of Drumore, PA, who was a schoolteacher. His death (ca. 1775) would make him of an appropriate age to be Patrick's father. If his will mentions a Patrick, then there may be hope that he is Patrick's father. This Samuel had bought land in Augusta County in the 1750s; coincidentally the same time that Patrick appears in the record as marrying Susannah Walker. There is also a Robert Porter of Drumore who died ca 1745, who had sons John, James, and Samuel. That DOD would fit our puzzle well. However, I have a sense that these Porters could be of a different line than our Patrick -- there is a patriarch Robert Porter in the Porter surname project at FTDNA who may be this Robert of Drumore, and my DNA does not match his. I am fairly confident that my DNA is the same or nearly so as Patrick's (allowing for mutation of fast-changing markers), since I closely match a sixth cousin, once removed, who descends from Patrick's son Samuel (I descend from John Walker Porter).
Porters of York County
I. John and Rose Porter, emigrants, born in England, came to Massachusetts Bay in 1628. In 1630 the members of the Windsor Church formed in Plymouth, England, in Margh of that year, came to and settled at Dorchester, Mass., on the first settlement of that town. In 1635 they removed to Maitteneaug, on the Connecticut river, now Windsor, and settled,that is. a company formed of them did so. In 1639 the Rev. Hewitt, or Huet, went there with another company, to join them, and with him went the Porters They died there, John on April 22d. 1648, and Rose in July, 1647. They had eleven children, among whom:
II. John Porter, settler, also born in England, in 1620. and died at Windsor, Goun., August 2. 1688. He married Mary Stanley, of Hartford, in 1650, then a resident of Hadley, Mase. She died September 13, 1688. They had twelve children, among whom
III. Samuel Porter, born March 5, 1664. at Windsor, Conn., but not accounted for there. It is believed he went to one of the Southern States. At the time there was considerable attraction to the Virginias (as Delaware, Maryland and West Virginia were then called). He left Connecticut and went southward; settled in the southern part of Chester county, Pa., where his family appear to have been prosperous and respectable, and were considered wealthy farmers in their day. 
And when the country west of the Susquehanna river was thrown open to settlers, two of his grandsons, Nathaniel and William Porter (brothers), crossed the river and settled in York now Adams) county. Black's cemetery at Upper Marsh Creek Presbyterian Church in Cumberland township, Adams county, Penna., contains monuments bearing these names and dates: Nathaniel Porter 1749; William Porter, 1753. and Violet Porter, 1735  These may have been Samuel Porter's children or grandchildren, or may have represented both.
IV. William Porter, born 1695, died August 3. 1749, owned and lived upon his father's homestead, and left several sons, among whom:
Nathaniel, born 1720. William, born 1729.
Commissioned a captain for the French and Indian War, February 8, 1747/8, in the Associated Regiment of Chester countv Pa. (see Pennsylvania Archives, second series, ii, p.506. He was then 53 years of age, and died the next year. His son, William, was then 28 years of age, and perhaps he was the one commissioned and not his father.
V Nathaniel Porter, b. 1720 in Chester county, Pa.; d. 1765 (as nearly as ascertained), in York (now Adams) county. Pa Married Sarah Maffitt, a lady of Scotch parentage, of Cecil county, Md. He settled on a tract of land in Cumberland township, about three miles south of where Gettysburg now stands. On this farm he lived until his death, which, as near as we have been able to ascertam, occurred in 1765. His wife died when their children were quite young. They had issue, several sons who married and went South, one son, who remained m Adams county, died unmarried; a daughter, who married, first, Robert McCreary, and secondly, Samuel Smith.
One of the sons, Nathaniel Porter (the youngest), was said to have been a soldier during the Revolution. He owned a farm in Mount Joy township (York), Adams County, Pa. (known as the Trestle Farm, since the beginning of the nineteenth century). Near the close of the eighteenth -century, Nathaniel Porter sold his farm and removed to Western Pennsylvania, where, owing to the great want of mail facilities, he was lost sight of by his friends. We have been unable to ascertain where he resided at the time of his death, but find that his family drifted Southward, and two of his sons, Joseph and James Porter, were prominet merchants and esteemed citizens of Nashville, Tenn. Joseph never married. Of James descendants or marriage as yet we know nothing
VI. William Porter, b. 1729, and d. in 1802. He was the youngest of the two brothers, who emigrated to Adams county, and was born in Chester county. He married Sarah Piercel, of Delaware, and settled on a tract of land in Adams county, near to the Maryland line. On this farm, now divided into two farms, he resided until his death. His wife survived him about six years. They lie buried in the graveyard of Toms Creek Presbyterian Church. They had six sons and several daughters: John, James, Nathaniel, Jeremiah, Richard, William, Mary (?), Ellenor, perhaps Elizabeth also.
A number of wills have been located for various Porters who were living in the general Octoraro area of Old Chester. Most of these wills were located by Ben Porter. His notes are found at Notebook:Porter Family in Old Chester County/Wills of Lancaster. Some wills are available in transcription, others currently only as images or PDF files. The following lists the wills that have been identified and for which information is available as MySource documents. Blue links will take you to a MySource document. Red links denote wills that for which information is available, but which have not been converted into MySource documents.
* Temporary summary waiting transcription
from: Abstracts of Cecil County, Maryland Land Records, 1734-1753 By June D. Brown [ Published by Heritage Books, 1999 ISBN 1585490385, 9781585490387 258 pages
Deed 1740 John Lusby and wife Margaret to Robert Porter 110 acers Hassel Branch on St. Albins Creek adhacebt tract called Freyers Hills
From Rootsweb 24 June 1788, Thomas Porter, decd., late of Drumore Township, Lancaster County, PA
His children, George (above 14), James (above 14), and Violet (above 14), choose James Greer of Drumore Township as their Guardian.
Lived in that part which became Little Britain Township.