I’m sure it was not a lottery. If they had to paid for the land the cost would not be less then .50 cents a acre and not more then $2. 00 dollars a acre the going rate was $1.25 acre
The address’s below are for page 210 A.-11, Page 211 is the title your land came under and page 210 A. & 11 is the Law that was passed on March 3, 1807, This info may come in handy.

http://memory.loc.gov/ll/llsp/029/0200/02240210.gif
http://memory.loc.gov/ll/llsp/029/0200/02250211.gif

I could not give all the info for the Silas family for they go way back.
If you would go to the web site of the ( L D S family Search ) you could find who the children married and their family’s you can also follow Silas and his wife Father and Mother and their father and mother and so on. Like I said this family goes way back.

I could not find any children for Joshua Mercer and Mary D. Mercer.
Mary D. ( Wells ) Mercer
b. May 11, 1790, Ga.
d. Sept. 17, 1880, Gordon, Henry Co. Al.

Silas Mercer, b. Feb. 1745, Currituck Bay, N. C., d. Aug. 1, 1796, Wilkes, Ga.
Father: James Mercer
Mother: Ann Jones
Married: Dorcas Green, 1768, Halifax N. C.
Children
1. F. Mary Mercer, b. abt. 1776, Wilkes Ga.
2. F. Mary Mercer b. abt. 1776, Halifax, N. C.
3. F. Nancy Mary Mercer b. 1777 d. 1777
4. M. Mourning Mercer b. abt. 1782 N. C.
5. F. Mourning Mercer b. abt. 1782 N. C.
6. M. Daniel Mercer b. 1780 N. C. d. Feb. 26, 1830 Ga.
7. M. Mount Moriah Mercer b. 1787 Wilkes Ga. D. 1822 Oglethorpe Ga.
8. M. Harmon Mercer : ( reverend ) b. 1784 N. C. d. Jan. 13, 1854
9. M. Mercer b. 1788 d. 1869
10. M. Joshua Mercer b. 1788 d. Feb. 4, 1869
11. F. Anna Mercer b. 1774 d. 1852
12. M. Jesse Mercer b. 1769 d. 1841

Note I know some of these names and dates don’t look right but the is the way they had it in the index.