| William Maclay | |
| State: | New York |
| Term Start: | March 4, 1843 |
| Term End: | March 3, 1849 |
| Term Start2: | March 4, 1857 |
| Term End2: | March 3, 1861 |
| Predecessor: | Aaron Wood |
| Successor: | Walter Underhill |
| Predecessor2: | Thomas R. Whitney |
| Successor2: | William Wall |
| Birth Date: | March 20, 1812 |
| Birth Place: | New York City, US |
| Death Date: | February 19, 1882 (aged 69) |
| Death Place: | New York City, US |
| Resting Place: | Green-Wood Cemetery |
William Brown Maclay (March 20, 1812 - February 19, 1882) was an American newspaperman, lawyer, and politician who served five terms as a United States representative from New York from 1843 to 1849, and from 1857 to 1861.
Born in New York City, he received private instruction and was graduated from the College of the City of New York in 1836. He was associate editor of the New York Quarterly Review in 1836, taught Latin, studied law, was admitted to the bar in 1839 and commenced the practice of his profession in New York City.
He was a member of the New York State Assembly from 1840 to 1842.
He was elected as a Democrat to the Twenty-eighth, Twenty-ninth, and Thirtieth Congresses, holding office from March 4, 1843, to March 3, 1849. He was an unsuccessful candidate for reelection in 1848 to the Thirty-first Congress, and was elected to the Thirty-fifth and Thirty-sixth Congresses, holding office from March 4, 1857, to March 4, 1861. He was not a candidate for reelection in 1860 to the Thirty-seventh Congress.
He in 1882 died in New York City. Interment was in Green-Wood Cemetery, Brooklyn.