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James Millholland (1812-1875) was a US railway engineer.
Credited with a number of important inventions, included the first box girder bridge (having girders comprising pairs of relatively deep side plates joined top and bottom by plate flanges), in April 1847. Description and drawing here.
However, unknown to Millholland, riveted wrought iron box girders were in use in the UK in 1840, on a road bridge designed by Andrew Thomson of Glasgow. The girders were relatively shallow (18" deep) and the box section was in the form of an isoceles trapezium.