Edgerton
A place-based surname, likely meaning someone from or near Egerton or a similar settlement name.
The #7,060 most common surname in the United States (2010 Census) — about 1 in every 65,136 Americans shares it.
Etymology
Edgerton is generally taken as a variant of Egerton, a surname from English place-names. The place-name element is usually explained as Old English personal name plus "tūn" meaning an enclosure, farm, or settlement, though older dictionaries often treat the surname simply as a local name. In practice, the surname likely meant "someone from Egerton" or a related place called Edge- or Egerton.
History
The historical sources you provided treat Edgerton as a local surname and explicitly point readers to Egerton. It appears in English-speaking records and later became established in the United States, where it is now most familiar as an American surname. Because the form is relatively uncommon, some bearers may descend from different but similar place-name lines that converged in spelling.
Origin
Regions
Variant spellings
Fun fact
The surname is close enough to Egerton that older reference works often treated Edgerton as just a spelling or local variant rather than a wholly separate name.
From the historical record
“Boston (U.S.X I, 30. Edgerton.— Local ; v. Egerton. Edgeworth.— Local, *of Edge- worth' : (i) a parish in co. Glouc, six miles from Cirencester ; (a) a township in co. Lancaster, five”
— A Dictionary of English and Welsh Surnames (alternate scan)