Source: U.S. Census Bureau  

Release: National Population Estimates  

Units:  Persons, Not Seasonally Adjusted

Frequency:  Annual, As of July 1

Notes:

This historical series may be used in conjunction with other population data to construct long time series. Caution should be exercise as the series contains breaks.
National population data for the years 1900 to 1949 exclude the population residing in Alaska and Hawaii. National population data for the
years 1940 to 1979 cover the resident population plus Armed Forces overseas.
National population data for all other years cover only the resident population. Estimates of the population including Armed Forces
overseas are as follows:

1919 105,063,000
1918 104,550,000
1917 103,414,000

National population data for the years 1900 to 1929 are only available rounded to the nearest thousand.

For more information see https://www.census.gov/population/estimates/nation/popclockest.txt

Source: Bank of England  

Release: A Millennium of Macroeconomic Data for the UK  

Units:  Thousands of Persons, Not Seasonally Adjusted

Frequency:  Annual

Notes:

Population of the Great Britain and North Ireland.

Break-adjusted measure intended for users who need a series without classification or geographical breaks for use in appropriate econometric work where, for example, the series will be log-differenced or log-linearised around a trend.

This series was constructed by the Bank of England as part of the Three Centuries of Macroeconomic Data project by combining data from a number of academic and official sources. For more information, please refer to the Three Centuries spreadsheet at https://www.bankofengland.co.uk/statistics/research-datasets. Users are advised to check the underlying assumptions behind this series in the relevant worksheets of the spreadsheet. In many cases alternative assumptions might be appropriate. Users are permitted to reproduce this series in their own work as it represents Bank calculations and manipulations of underlying series that are the copyright of the Bank of England provided that underlying sources are cited appropriately. For appropriate citation please see the Three Centuries spreadsheet for guidance and a list of the underlying sources.