The immigration point of Castle Garden was located in New York harbor and predates Ellis Island. Castle Garden was active from 1830 to 1890. Although the primary port of entry to the United States at this time it is a good place to check if you suspect this to be where your ancestors entered the country. This site is very similar to the Ellis Island site.
Be sure to use wild cards when doing your search. The print quality of the records in some cases can be poor and the hand writing can be a challenge. Variances in the spelling from the name you know to how they are written abound. The website is castlegarden.org.
Remember to make copies for your documentation.