Trying to find thompson family tree! help!?

all i know is that: Rachel ragsdale (great great great grandmother) married dewit thompson (g. g. g. grandfather) and i know from like the 1900's and up but i cannot find any information past that and 1900's is pretty recent when it comes to geneology. what are some websites to track geneology that... show more all i know is that:

Rachel ragsdale (great great great grandmother) married dewit thompson (g. g. g. grandfather) and
i know from like the 1900's and up but i cannot find any information past that and 1900's is pretty recent when it comes to geneology.

what are some websites to track geneology that WORK that i DONT PAY FOR! sorry but im 18 and have no money to put towards this and it would just frustrate me.

where can i find the thompson family tree???????
Update: if you could check the names that would be great!!!! ok so

dewit thompson and rachel ragsdale lived in illinois and there son is troy thompson. this would be along the 1890-1910 for the birth
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