| 37141 | March 31 | Holiday and observance | Thomas Mundy Peterson Day (New Jersey) |
| 37142 | March 31 | Holiday and observance | Transfer Day (US Virgin Islands) |
| 37143 | March 31 | Holiday and observance | César Chávez Day (United States of America) |
| 37144 | March 31 | Holiday and observance | International Transgender Day of Visibility |
| 37145 | April 1 | Event | 286 – Emperor Diocletian elevates his general Maximian to co-emperor with the rank of Augustus and gives him control over the Western regions of the Roman Empire. |
| 37146 | April 1 | Event | 325 – Crown Prince Jin Chengdi, age 4, succeeds his father Jin Mingdi as emperor of the Eastern Jin dynasty. |
| 37147 | April 1 | Event | 457 – Majorian is acclaimed emperor by the Roman army. |
| 37148 | April 1 | Event | 527 – Byzantine Emperor Justin I names his nephew Justinian I as co-ruler and successor to the throne. |
| 37149 | April 1 | Event | 528 – The daughter of Emperor Xiaoming of Northern Wei was made the "Emperor" as a male heir of the late emperor by Empress Dowager Hu, deposed and replaced by Yuan Zhao the next day she was the first female monarch in the History of China, but not widely |
| 37150 | April 1 | Event | 1293 – Robert Winchelsey leaves England for Rome, to be consecrated as Archbishop of Canterbury. |
| 37151 | April 1 | Event | 1318 – Berwick-upon-Tweed is captured by the Scottish from England. |
| 37152 | April 1 | Event | 1340 – Niels Ebbesen kills Gerhard III, Count of Holstein-Rendsburg in his bedroom, ending the 1332-1340 interregnum in Denmark. |
| 37153 | April 1 | Event | 1545 – Potosí is founded after the discovery of major silver deposits in the area. |
| 37154 | April 1 | Event | 1572 – In the Eighty Years' War, the Watergeuzen capture Brielle from the Spaniards, gaining the first foothold on land for what would become the Dutch Republic. |
| 37155 | April 1 | Event | 1625 – A combined Spanish and Portuguese fleet of 52 ships commences the recapture of Bahia from the Dutch during the Dutch–Portuguese War. |
| 37156 | April 1 | Event | 1789 – In New York City, the United States House of Representatives holds its first quorum and elects Frederick Muhlenberg of Pennsylvania as its first Speaker. |
| 37157 | April 1 | Event | 1826 – Samuel Morey received a patent for a compressionless "Gas or Vapor Engine." |
| 37158 | April 1 | Event | 1833 – The Convention of 1833, a political gathering of settlers in Mexican Texas to help draft a series of petitions to the Mexican government, begins in San Felipe de Austin |
| 37159 | April 1 | Event | 1854 – Charles Dickens' novel Hard Times begins serialisation in his magazine Household Words. |
| 37160 | April 1 | Event | 1865 – American Civil War: Battle of Five Forks. Union Army led by Philip Sheridan decisively defeated Confederate States Army led by George Pickett, leading to Breakthrough at Petersburg and Appomattox Campaign. |
| 37161 | April 1 | Event | 1867 – Singapore becomes a British crown colony. |
| 37162 | April 1 | Event | 1871 – The first stage of the Brill Tramway opens. |
| 37163 | April 1 | Event | 1873 – The White Star steamer RMS Atlantic sinks off Nova Scotia, killing 547 in the worst marine disaster of the 19th century. |
| 37164 | April 1 | Event | 1887 – Mumbai Fire Brigade is established. |
| 37165 | April 1 | Event | 1889 – The University of Northern Colorado was established, as the Colorado State Normal School. |
| 37166 | April 1 | Event | 1891 – The Wrigley Company is founded in Chicago, Illinois. |
| 37167 | April 1 | Event | 1893 – The rank of Chief Petty Officer in the United States Navy is established. |
| 37168 | April 1 | Event | 1908 – The Territorial Force (renamed Territorial Army in 1920) is formed as a volunteer reserve component of the British Army. |
| 37169 | April 1 | Event | 1918 – The Royal Air Force is created by the merger of the Royal Flying Corps and the Royal Naval Air Service. |
| 37170 | April 1 | Event | 1919 – The Staatliches Bauhaus school is founded by Walter Gropius in Weimar. |