I want to add demographic data to a data set. Any suggestions on where to find zip code level data? Ideally, I would like to add demographic features to my data.  I have zip codes for each observation, so I was hoping to add in the demographic data by zip code.  Unfortunately, I cannot find any demographic data by zip code.  

Does anyone have any suggestions on using the zip code tabulation area data for zip codes? 

Thanks!
The US Census American Community Survey can provide a lot of demographics by different geographies, including zip. Check out:

https://factfinder.census.gov/