Showing skyline of Manhattan from Jersey City. Manhattan Island 19.65 Square miles, was purchased in 1626 from Indians for about 524.00, land value now $4,020,000,000. total realty value with improvements, is $6,075,000,000. an average of $432,000. per acres. The Island has 2,3331, 542 inhabitants, the lower end has an office population of 400,000 land there is worth from $200 to $600 per square foot and office space rents at from $1 to $40 per square foot.