Closure of US equine slaughter facilities in 2007 along with the concomitant economic recession have contributed to a sharp increase in the number of unwanted horses throughout the United States, with estimates totaling 100,000 horses per year. The objective of the study was to obtain comprehensive data regarding nonprofit organizations caring for unwanted horses, along with the characteristics and outcome of horses relinquished to these organizations. Nonprofit organizations that accept relinquished equines were contacted to participate in a 90-question survey. Responding organizations (144 of 326 eligible) in 37 states provided information on 280 cases representative of the 7,990 horses relinquished between 2007 and 2009. Data collected characterized these organizations as being in existence for 6 yr, financially supported through donations and personal funds, dedicated to the care of only 10 to 20 horses on a property of just over 30 acres, and reliant on volunteers for help. Funding was the greatest challenge to continued operation of nonprofit equine organizations, with maintenance costs for the care of a relinquished horse averaging $3,648 per year. Financial hardship, physical inability, or lack of time to care for the horses by owners were the most common reasons for relinquishment, followed by seizure through law enforcement agencies for alleged neglect or abuse. Relinquished horses consisted of mostly light horse breeds (79.3%), with Thoroughbreds and Quarter Horses as the most represented breeds. The age of relinquished horses ranged from 3 d to 42 yr old (12.4 ± 0.5 yr). About one-half of the horses entered in the survey were considered unhealthy due to illness, injury, lameness, or poor body condition. For every 4 horses relinquished to a nonprofit organization, only 3 horses were adopted or sold between 2006 and 2009, and many organizations had refused to accept additional horses for lack of resources. The estimated maximum capacity for the 326 eligible registered nonprofit equine rescue facilities of 13,400 is well below the widely published estimate of 100,000 horses that become unwanted in the United States every year. Nonprofit equine rescue and sanctuary facilities have historically played an important role in safeguarding the welfare of horses in society, but funding and capacity are limiting factors to their potential expansion in continuing to care for the current population of unwanted and neglected horses in the United States.