There is an Alexander McKelvey in the 1820 census in Frederick Town, Frederick Co. (not Cecil), Maryland.He appears to be over age 45 (census hard to read), with children ranging in age from less than 10 to 26-45 (males) and females less than 10, 10-16 and 26-45, plus probably the wife over age 45.
If Alexander was born in 1786, he would be age 34 in 1820 and could be the son age 26-45, but who are the over age 45 male and female - his parents - father also named Alexander??
I do not find a McKelvey listed in Maryland earlier than 1820.
Also, you wrote: Parents of Andrew Mckelvey b 16 Jun 1814 Ireland, died 20 Feb 1940 in Union, Jasper, MO, who married Allie Frame on 20 Feb 1840 in PA.
This is confusing - 1940?? and died and was married on the same day??