Using the Trans-Atlantic Slave Trade Database / Voyages, this can be answered pretty quickly. (Go play with the site--it's really very enlightening!) The database itself is the product of a number of institutions (educational and government) and represents decades of work, and is pretty reliable within the caveat that its reliability can only reflect the source material that is available. However, the general trendlines are solid and illicit trade is far smaller than the legal trade was on the Atlantic side, even after the trade's abolition.

So what does the information say? Well, for mainland North America (taken in the DB to be the modern-day US, including foreign holdings) the lowest number is around 390,000 overall. The curve of registered disembarkations is interesting [edit: by decades here, though the TSTDB can do annual as well]:

Mainland North America

• 1628-1630 100
• 1631-1640 0
• 1641-1650 0
• 1651-1660 1,064
• 1661-1670 2,289
• 1671-1680 2,455
• 1681-1690 2,554
• 1691-1700 6,684
• 1701-1710 13,131
• 1711-1720 12,679
• 1721-1730 36,838
• 1731-1740 62,181
• 1741-1750 21,144
• 1751-1760 42,947
• 1761-1770 46,691
• 1771-1780 31,185
• 1781-1790 14,298
• 1791-1800 14,388
• 1801-1810 72,978
• 1811-1820 4,635
• 1821-1830 91
• 1831-1840 0
• 1841-1850 0
• 1851-1860 413
• Total overall 388,747

This matches other regions in the existence of a big "bump" in the 18th century, but for the US is particular in the early decades (expansion of planting) and the decades just before the Revolutionary War and right after 1800, the latter likely because of the impending termination of the legal trade and a brief window of relative peace amidst the Napoleonic Wars that allowed the trade to proceed. The US however was one of the regions where local births and slave trading internally produced population growth, so it would be interesting to map this against the internal slave trade and slave populations overall.