Depending on the time frame you need you may just have to use your nearby Latter Day Saints (LDS) Family History Center (Mormons). They have microfilmed records from all over the world including the Dutchess County NY Land records (Deeds, Mortgages)
Go to www.familysearch.org
Click on Catalog type in Dutchess, click on the New York, Dutchess, hit search. Then select New York, Dutchess - Land and Property
Then select Deed Records - 1781-1901 and see a list of what is available to order/rent.
You'll want to start with the index first -- there are two one by seller and one by buyer. Once you find the person in the index it will give you a volume and page number. Mortgages are set up the same way.
The catalog is a beta version so if it doesn't seem to be working, from the main page on the right, click on previous version and use that catalog on the old website.
So you use the catalog to get the microfilm numbers you need. To place a rental order at https://www.familysearch.org/films/
, you need to create a login id for familysearch and make sure to select the family history center that is closest to you so they know where to send the order. You pay by credit card or paypal.
Since earlier this year you have to place film/fiche rental orders online unlike before when you had to go there place the order and then come back when the film/fiche arrived. If you haven't been to your nearest LDS FHC perhaps visit it first to get a lay of the land so to speak before you place an order. If you are in a more populated area you may have a couple LDS FHCs to choose from. You may want to investigate and compare days/hours open as each operates based on volunteer/staff availability.