Bills of sale might be recorded in Deeds for the County in which the transaction took place.
If Denton Jacques is a son or relative of Lancelot Jacques, they did not initially settle in 'Western Maryland.' According to Frederick, Co, MD deeds a Lancelot Jacques was a merchant of Annapolis in the 1750s. In the 1760s he and a partner bought some land recorded in Frederick Co. that might have become part of Washington Co. when it was set off.
After the Rev. War one Denton Jacques and a Lancelot Jacques were acquiring grant land in present Washington Co, and a Denton Jacques was assessed taxes for 1783 in Washington Co. MD on 'sundry tracts' in various areas of the County.
I did not look at Washington Co. deeds indexes for Jacques family transactions during the war, but you can. They are available free on the internet in a site operated by the Maryland Archives. Go to www.mdlandrec.net
and register; once you get a password after a few days you can look at the deeds indexes for all MD counties and deeds themselves for all but Washington Co.
Grants are indexed by the MD Archives at a site www.plats.net
(username is plato, password is plato#, all lower case). You have to click through three pages to get to the search box: click the top line including the word 'condominiums' on the first, and on the next page click 'advanced search' under the boxes. Be sure to check a variety of spellings, these indexes were very peculiarly put together. In the three right-hand columns of your search results are links to the Archives' peculiar view of helpful information. The 2d and 3rd columns *from* the right usually have '0' but if you see one with a number that means images of the survey documents are accessible directly: click the far-right link to get to the page where you can download them.
Note that ownership does not denote residence on the land. You are looking for bills of sale, for deeds that may spell out contracts or partnerships, and deeds that may give a background story on why the transaction is taking place. You might find something indicating a sale related to war supplies.
The MD Archives' problems with getting the Washington Co. deeds' images posted is a dreadful story. But if you find something you want to look at in the indexes you can at least write the Archives for copies.
Also helpful is the series of published abstracts of Frederick Co. deeds by Patricia Abelard Andersen. Unlike the deeds indexes her abstracts have every-name indexes and lists of the places and tract names mentioned in the deeds. As you get familiar with the territory these can be very helpful. You can find these books by an internet search of the author's name.
The 1783 tax list for Washington Co. MD is available at the MD Archives' main site, scroll through the Volume listings toward the end (they make it impossible to find these lists using their search engine).
The MD Archives' online search engine might, however, be useful if you do name searches.