I have a neat map book (new toy!) called "Map Guide to the US Federal Censuses, 1790-1920" by Wm. Thorndale & Wm. Dollarhide (Genealogy Pub. Co., Inc., Baltimore 1987, ISBN 0-8263-1188-6). I don't remember what I paid for it, but it's already proved its worth!
The layout of the southern central counties in KY goes something like this:
1790: the entire south-central (SC) KY area was Lincoln Co.
1800: From W>E: Christian Co. contained Trigg, Christian & most of Todd Counties; Logan Co. contained western edge of Todd, Logan, southern part of Butler, and western part of Simpson counties; Warren Co. contained eastern part of Simpson, Warren, southern part of Edmondson (so. of the Green Riv.), western part of Barren and western part of Allen counties; Barren Co. contained southern part of Hart (so. of the Green Riv.), Barren, western part of Metcalfe & western part of Monroe counties; Green Co. contained most of Green, Taylor, Adair, western tip of Metcalfe, and most of Russell, and the very eastern parts Casey & NW Wayne counties; Cumberland Co. contained eastern Monroe, all of Cumberland & Clinton, and most of western Wayne Co.
1810: from W>E: Christian Co basically unchanged from 1800; Logan Co. contained eastern Todd, Logan & western Simpson counties; Warren Co. contained eastern Simpson, Warren, western Allen, southern Edmonson (so. of the Green Riv.) and western edge of Barren counties; Barren Co. contained southern Hart (so. of the Green Riv.) Barren, eastern Allen, western Monroe, and most of Metcalfe counties; Green Co. contained Green and Taylor counties and the NE tip of Metcalfe county; Adair Co. contained the western part of Casey, Adair, eastern Metcalfe and most of Russell counties; Cumberland Co. contained eastern Monroe, Cumberland, and SW Russel and most of Clinton counties; Wayne Co. contained a little bit of SE Russell, eastern Clinton, Wayne Co. and western McCreary counties.
1820: From W>E: Trigg Co (mostly as it is today); Christian Co.; Todd Co. (mostly as it is today); Logan Co. (mostly as it is today); Simpson Co. (mostly as it is today); Warren Co contained southern Edmonson (so. of Green Riv.) and western tip of Barren; Allen Co. (mostly as it is today); Barren contained Barren and western part of Metcalfe county; Monroe Co (mostly as it is today); Hart Co. contained eastern Edmonson Co and Hart Co.; Green Co. contained Green & Taylor counties and the NE tip of Metcalfe Co.; Adair Co. contained eastern Metcalfe, Adair, most of Russell and western part of Casey Co.; Cumberland Co. contained Cumberland & most of Clinton Co.; Wayne Co. contained SE Russell, NE Clinton, Wayne & western McCreary counties.
1830: W>E: Trigg as it is today; Christian as it is today; Todd as it is today; Logan mostly as it is today, with western edge of Simpson Co; Simpson mostly as it is today; Warren as it is today; Edmonson as it is today; Allen as it is today; Hart as it is today; Allen as it is today; Green Co. contained Green & Taylor counties; Barren contained Barren and most of Metcalfe Co.; Monroe mostly as it is today; Cumberland contained Cumberland and most of Clinton county; Adair contained Adair, eastern Metcalfe and western Casey counties; Russell as it is today; Wayne Co. contained eastern Clinton, Wayne & western McCreary counties.
1840: W>E: Trigg, Christian Todd all as they are today; Logan & Simpson are unchanged from 1830; Warren, Allen, Edmonson, Hart, Barren, Monroe, Green, Adair, Russell & Wayne are unchanged from 1830; Clinton Co. & Cumberland Co. as they are today.
1850: W>E: All counties the same as 1840; Green & Taylor are separate counties
1860: W>E: All counties the same as 1850; Metcalfe is a separate county (its lines are still changing though)
1870: W>E: All counties the same as 1860
1880: W>E: All counties the same as 1870, Metcalfe still contains a bit of NW Cumberland Co.
1890-1920: All counties unchanged, except McCreary Co. is created in 1912 from Pulaski, Wayne & Witley counties.
Hope this helps locate the time & place your relations were living ....
Be well & God bless,
Kate Beaugrand Cook