Actually, there is a Cecil County, MD and a Cecil Co., DE but I was mistaken when I said the Alexanders settled in Cecil Co., DE. I meant Maryland.
An interesting article about one Alexander in particular can be found by searching online Wikopedia for 'Alexanders in Cecil County, Maryland'. Here is a bit of abstract from the article:
Robert Alexander (Maryland)
Robert Alexander was born on his family's estate at Head of Elk in Cecil Co., MD about 1740. Educated to the law and admitted to the bar, he practiced in Baltimore.... From 1774-1776 he attended the Annapolis Convention as a representative of Baltimore Co. He also represented Baltimore in the state's Committee of Safety.
On December 9, 1775 the Convention named Alexander one of their delegates to the Continental Congress. He attended sessions starting in January 1776, and on January 16 the Congress added him to their Secret Committee. Then in April he was added to the Marine Committee.... After the promulgation of the Declaration of Independence, he sailed for England with other Baltimore loyalists. When the British moved north towards Philadelphia he accompanied them, and was never to return. By the summer of 1778, when Howe abandoned the occupation of Philadelphia, Alexander fled to the Royal Navy, and made his way to London in 1782.
In 1780, the State of Maryland judged Alexander guilty of high treason, and seized most of his property. His estate became the town Elkton, Maryland, although the wife he had abandoned was allowed to keep the main house that his father had built in 1735. The house still stands, and is located at 323 Hermitage Drive in Elkton. Alexander died in exile in London, England on November 20, 1805.
But going back to the earliest 'documented' record I've found (so far) of any Alexanders in America, would be a John Alexander, who, according to some family trees on Ancestry.com died in 1677 and had at least three sons; John, Robert and Phillip. I have not verified this information)
Robert Alexander, (the oldest son and heir of John Alexander mentioned above) lived in Stafford Co., VA, and was married to Priscilla Frances Ashton. He died prior to 1 June 1704 and had at least one son, Robert Alexander, who had a son named Charles Alexander.
I've compiled a few notes regarding this line of Alexanders from information that I found in 'Maryland's Heraldic Families'. (MY notes are in parenthesis):
John Alexander (Sr.) was born in Glasgow, Scotland and died in Virginia. Married 1st to ----- (Catherine) Graham, daughter of John Graham. Married 2nd to Mrs. Tabitha Smart. Immigrated to America in 1659 in the company of Littleton Scarburgh and (sister) Tabitha Smart, children of Col. Edmond Scarburgh (who obtained a grant of 1500 acres in Northampton Co., VA on March 24, 1659).
In 1664, this John ALEXANDER, obtained a grant for 1450 acres formerly granted to John Bagnall and John Walter. In 1664, John ALEXANDER Sr. also patented land in Westmoreland County on Atoppin Creek. Children: (Capt.) John Alexander Jr., who married ---- Pitzhugh, dau. of Philip Pitzhugh and died without issue; Charles; a daughter unnamed that married Thomas Pearson; Robert born 1704 who married Priscilla Francis Ashton, dau. of John Ashton; and Philip born 1705 (Stafford Co., VA), who married Sarah Ashton, another dau. of John Ashton.