Here is a list of National Organizations that provide Down Syndrome resources:

National Down Syndrome Society (NDSS)
The mission of the NDSS is to be the national advocate for the value, acceptance and inclusion of people with Down syndrome.

National Down Syndrome Congress (NDSC)
The NDSC works to create a national climate in which all people will recognize and embrace the value and dignity of people with Down syndrome.

Global Down Syndrome Foundation (GDSF)
GDSF is dedicated to significantly improving the lives for people with Down syndrome through research, medical care, education and advocacy.

LuMind IDSC Foundation
LuMind’s mission is to stimulate biomedical research that will accelerate the development of treatments to significantly improve cognition, including memory, learning and speech, for individuals with Down syndrome so they can: participate more successfully in school, lead more active and independent lives and avoid the early onset of Alzheimer’s disease.

International Mosaic Down Syndrome Association
IMDSA is designed to provide support, information and research to anyone whose life has been affected by mosaic Down syndrome.

Spread the Word to End the Word
Campaign to raise awareness about the hurtfulness of the r-word.

DS-Connect: Down Syndrome Registry
The registry links those seeking volunteers for their research studies with those who most stand to benefit from the research.

Social Security Disability Resource Center (SSDRC)
SSDRC informs how the Social Security Disability and SSI Disability process works from start to finish.

Wrightslaw
Wrightslaw provides accurate and reliable information about special education law, education law, and advocacy for children with disabilities.