Nyland and Tavastehus County (Swedish: Nylands och Tavastehus län, Finnish: Uudenmaan ja Hämeen lääni) was a county of the Swedish Empire in Finland from 1634 to 1809.
In 1775 whole northest part of the county (later Central Finland region) was transferred to the new Vasa County. Also a part of historical Satakunta was added to the Nyland and Tavastehus County from the Åbo and Björneborg County, while Upper Hollola was transferred to the new Kymmenegård County.
By the Treaty of Fredrikshamn in 1809 Sweden ceded all its territories in Finland, east of the Torne River, to Russia. The county still continued to exist as a province of the new autonomic Grand Duchy of Finland until 1831, when it was split to Häme Province and Uusimaa Province.
Provinces of Finland 1634: 1: Turku and Pori, 14: Nyland and Tavastehus
, 18: Ostrobothnia, 20: Viborg and Nyslott, 21: Kexholm
Provinces of Finland 1776: 1: Turku and Pori, 4: Vaasa, 10: Oulu, 14: Nyland and Tavastehus
, 15: Kymmenegård, 16: Savolax and Karelia
Provinces of Finland 1831: 1: Turku and Pori, 2: Uusimaa
, 3: Häme
, 4: Vaasa, 6: Mikkeli, 8: Kuopio, 10: Oulu, 13: Viipuri