I am descended from a Slifer family which settled in this general area before the Revolution. I have a giant heap of data on my own branch but only bits and pieces from the beginning of other branches. Alas, I do not come down as far as your Nathan, so we have to search for the missing link. I will try to help, but may just make your head spin.
When you write "of Richland Township," do you mean that he was born there?? Or could it be that he migrated a dozen miles or so looking for a farm to buy??
On the assumption that he was born there, his family should appear in the 1820 census. There is a John Slifer family listed, with two children in the household under 10 years of age, one boy and one girl. The puzzlement is that the only adult woman is over 45 years of age and more likely to be the grandmother of the two youngest children. What happened to their mother?? There are two males in the 16-26 range, one of which could very well be their father.
What appears to be the same household is listed in the 1810 census with both adults shown as 26-45. This implies that they were born about 1770. I do have a Johannes Schleiffer born in 1771 whose wife was born in 1766, per tombstones.Their tombstones are located at East Swamp Church (Mennonite)in Milford Township but essentially on the township line, a hop and skip from Richland Township.
There will be considerable work to do fleshing out this shaky connection. There is a reward at the end of the tunnel however; I have traced this tribe of Slifers back into the end of the 16th Century at a farming community in the foothills of the alps above Zurich. The Swiss spelling of the surname is Schleipfer!!