Butterflies of Castro County, Texas
- Information about and pictures of all the known species of butterflies in the county.
- http://www.butterfliesandmoths.org/map?dc=1506&_dcc=1&si=44

Capitol Impact: Castro County
- Political, economic, and educational data.
- http://www.capitolimpact.com/gw/cntydetail.asp?state=tx&stfips=48&stname=Texas&fips=48069

Handbook of Texas Online : Castro County
- Current and historical information about Castro County.
- http://www.tsha.utexas.edu/handbook/online/articles/CC/hcc8.html

Castro County, Texas - TXGenWeb Project
- USGen Web project - Castro County.
- http://www.rootsweb.com/~txcastro/castro/

The Political Graveyard: Castro County
- Lists politicians who lived or died in the county.
- http://www.politicalgraveyard.com/geo/TX/CT.html

Amphibians and Reptiles in Castro County
- Texas Cooperative Wildlife Collection list of species found in the county.
- http://wfscnet.tamu.edu/tcwc/checklist/CASTR035.HTM