At the end of the Livonian Crusade (1208–1227 in Estonia), both counties were captured by the Order of the Sword Brothers until given back to Denmark with the Treaty of Stensby in 1238.

In 1561, after the outbreak of the Livonian War, the nobility of North Estonia and the Tallinn Town Council declared loyalty to Sweden.

Russian forces finally arrived in 1710 and laid siege to Tallinn for a month until the Swedish garrison surrendered, thus ending the Great Northern War in Estonia.

The plague raged on for several years, eventually leaving several parts of the county completely empty of human habitation.

Imperial Russian rule started with the construction of naval harbours in Tallinn and Paldiski (Swedish: Rogerwiek).

In 1870, the Paldiski-Tallinn-St. Petersburg Railway was opened, after which several smaller settlements along the line - Paldiski, Keila, Saue, Nõmme, Aruküla, Raasiku, Kehra and Aegviidu (then in Viru County) - started to grow.

In December 1917, Russian sailors under the leadership of Stepan Maximovich Petrichenko declared the "Soviet Republic of Soldiers and Fortress-Builders of Naissaar".

During the Estonian War of Independence, Soviet troops were halted only 40 km east of Tallinn by the end of 1918.

The submarine eventually made her way to the United Kingdom, which led both the Soviet Union and Germany to question Estonia's neutrality.

With its new military bases in Northern Estonia, the Soviet Union invaded Finland on 30 November 1939, starting the Winter War.

During 1939–1940, most of the Baltic German population from Tallinn and the Harju County countryside fled to Germany (Umsiedlung).

Soviet bombers shot down the passenger airplane "Kaleva" near Keri island, killing all nine on board, which had included foreign diplomats.

On 16 June 1940, the Red Army invaded Estonia and organised a Soviet coup d'état in Tallinn.

On 21 June 1940, the Independent Signal Battalion in Tallinn showed resistance to the Red Army, until it surrendered and was disarmed on the same day.

The Erna long-range reconnaissance group was sent from Finland to Northern Estonia on 10 July 1941 to perform reconnaissance of the retreating Red Army, but it eventually engaged the destruction battalions near Kautla forest (Battle of Kautla) on 31 July to 1 August 1941, allowing 2,000 civilians to flee.

In September 1942, up to three thousand foreign Jews and Gypsies were executed at Kalevi-Liiva in Jõelähtme Parish, while the rest were sent to the small Jägala concentration camp nearby, that never had more than 200 prisoners as their lifespan was short.

Klooga concentration camp in Keila Parish was mostly evacuated before the Soviet takeover, however, 2,000 prisoners were executed before the German retreat.

Tallinn was bombed by the Soviet Air Force on 9 and 10 March 1944, killing 757 people and destroying 8,000 buildings (about one-third of the capital).

The National Committee of the Republic of Estonia was formed in Tallinn in March 1944 and the last Prime Minister of Estonia Jüri Uluots organized a new government under Otto Tief on 18 September 1944, captured government offices in Tallinn on 20 September 1944, and put the Estonian flag on top of the Pikk Hermann Tower.

German forces started Operation Aster to evacuate its 50,000 soldiers and 20,000 civilians through Tallinn and Paldiski.

Before the Soviet reoccupation in 1944, thousands fled to Sweden across the Baltic Sea, including the entire Estonian Swedish population, who had been settling also on Pakri islands in Harju County.

Soviet rule brought major changes in rural municipalities as local village councils were created throughout 1945.

On 31 December 2021, there were 614,567 people living permanently in Harju county, which was 11.2% more than at the same time ten years ago.

The EELC's East-Harju Deanery includes the congregations of Harju-Jaani, Jõelähtme, Jüri, Kose, Kuusalu, Leesi, Loksa, Prangli, Randvere, Rannamõisa and Tuhala.

The congregations belonging to the Catholic Church in Estonia that operate in Harju County are: are the Tallinn St.

[9] There are also congregations of Moravian Church (or Unitas Fratrum) in Harju County: Tallinn Endla, Harku, Kuusalu, Nabala, Nissi and Saku-Tõdva.

There are also several long sand beaches, for example Kakumäe, Stroomi in Pelguranna, Pikakari in Paljassaare and Pirita along the shoreline and Lake Harku in Pikaliiva, all within Tallinn, and Kloogaranna and Kaberneeme in the countryside.

The shoreline is also characterized by many peninsulas, such as Pakri, Lohusalu, Suurupi, Kakumäe, Kopli, Paljassaare, Viimsi, Ihasalu, Kaberneeme, Juminda and Pärispea.

The park was intended for the protection of the natural and cultural heritage of the coastal landscapes of Northern Estonia.

Harju County and Estonia are serviced by Lennart Meri Tallinn Airport, which is open to both domestic and international flights.