Final answer:
New York City had the largest population on the East Coast in 1870, driven by transportation advancements and a surge of immigrants.
Step-by-step explanation:
The city located on the East Coast that had the most people living in or near it in 1870 was New York City. The population data from the era clearly show that New York had a significant lead in population growth, far surpassing the other cities listed. In 1860, New York's population was already at 1,174,800 and by 1880, it had grown to 1,912,000, which indicates that by 1870, New York was most likely the city with the largest population on the East Coast. The growth was due to various factors, including advancements in transportation like the opening of the Erie Canal and the influx of immigrants, contributing to the city's rapid expansion and making it a bustling hub for commerce and industry.