That number is likely under-reported, and there has been a significant rise in the number of people who feel comfortable identifying in the past few years. A study performed in 2017 found that 2.7% (of roughly 80,000 surveyed) identified as trans or gender non-conforming: https://pediatrics.aappublications.org/content/pediatrics/14...
I've seen the numbers that range from ~1% (or a little under) to as much as 3%, like the study above.