The first religious "system" of belief was the Nordic mythology including many deities like Oden (Odin), Tor, Freja, Balder, Höder, This was probably fairly uniform throughout the Nordic countries. There are many remnants from these beliefs still around today but the origin is unknown to many. Not only do we find hällristningar (rock carvings), runstenar (rune stones) and blotplatser (offering sites) in nature but we still use place and person names,  weekdays, proverbs and more referencing the deities and customs of the heathen period. This includes not only the Nordic region but also most of the (old) English speaking world as well. Just think of Thursday = the day of the god Thor.

Christianity came to the Nordic countries in the 9th century though traders. The first known "regular" missionary was the roman-catholic Ansgar, who visited the trading place of Birka (in lake Mälaren, north of today's Stockholm) but the more general spreading of the new faith started with the formal christening of the king Olaf Skötkonung who reigned around the year 1000 in province Västergötland and his creation of a bishopric in Skara (Västergötland province, south of lake Vänern). Its first bishop was named Turgot.
After many years of disputes the Christianity takes over at the beginning of the 12th century and it is now that the formal religious and worldly organization is created with the divisions into stift (dioceses) (Skara in province Västergötland was the first) and församling (parishes) (more details about that here).
In 1120 the following bishops are documented: Skara, Linköping, Tuna, Eskilstuna, Strängnäs, Sigtuna and Västerås, later also Växjö and Åbo (in Finland).
The first archbishops were in the city of Lund in Skåne province which at the time was in Denmark. The first Swedish archbishop, Stefan av Alvastra, was appointed in Old Uppsala city in 1164.

The first known church laws are known from the landskapslag (provincial laws) from province Uppland (north of Stockholm). These laws were created in each province (written down in the 13th century) before Sweden was united to one realm and the laws from province Uppland were accepted by a national church convention to be valid for all Sweden.
The first national laws for all Sweden were enforced from 1350 (Magnus Eriksson)
At the meeting in Skänninge 1248 the "kanonic" law was accepted for the church and the church was permitted to receive donations of money and property. With the Alnö stadga in 1280 the exemption from state tax for the church and knights was established and thus the terms frälse and nobility appeared. Those two legislations formed the basis for the great wealth that the church then quickly achieved.

Reformation - the move from Catholic to Protestant faith

Under the reign of King Gustav Vasa, who instigated the "reformation" (including the confiscation of most church property), the church laws were revised by the parliament at Västerås in 1527. This is the turn from Roman-Catholic to Evangelical Lutheran faith.
The process to establish the faith and the new order all over Sweden took many years, partly because king Johan III preferred variations of protestant faith (Calvinism / Reform Catholicism) but was officially concluded at the Uppsala möte (meeting at Uppsala) in 1593 in opposition of the Catholic king Sigismund (son of Johan III) but with strong support from then Duke Karl (from 1604 king Karl IX, brother of Johan III).
In the next century this faith became the only one allowed and joined with the Swedish State.

This is a comprehensive law regulating most aspects of the church organization and practice. First of all it states what is the "correct" faith (Evangelical-Lutheran). The church services at mass, christening, communion and funeral, how to elect priests and bishops, as well as church staffing and care of church property is regulated. It is here the instructions about the church records are written and the reason that Sweden has such a rich treasure of records from old times. In several areas it took many years before a regular practice was established and recording may have started as late as a couple of decades into the 18th century in some places even though the law was officially valid as of 1688.
When this law was replaced by a new church law in 1992 it had been in effect for 304 years.

With the growing pietistic movement in the early 18th century the state church passed a law against the practice of private religious meeting, called konventikel. The law states that only the parish priest could lead religious meetings except for the head of family leading a devotion with his family, a practice called husandakt. The punishment for arranging  a religious meeting was a fine or even a jail sentence.
This law also confirms the duty of the parish priest to arrange yearly husförhör (see below).
The konventikelplakat was repealed in 1858.
With this law out of the way several new religious movements could prosper. Some of those groups were however not accepted by the contemporary society and certainly not by the church so many people emigrated as groups such as the "jansonites" to Chisago Lake area, USA.

In the 19th century several Christian revival movements developed within Svenska Kyrkan (the state church). The major ones in Sweden were:
Schartauanismen, laestadianismen and Evangeliska Fosterlandsstiftelsen.

Outside the state church the main movements were :
Svenska baptistsamfundet (Baptist)
Metodistkyrkan (Methodist)
Svenska Missionsförbundet and 
Frälsningsarmén (the Salvation Army).

Not until 1860 was it possible to leave the Svenska Kyrkan and still only to enter another evangelical movement.
In 1951 the law about religious freedom was passed and it became possible to leave Svenska Kyrkan without joining another movement. In that law it was also stated that Svenska Kyrkan was a religious society and no longer part of the state. The final separation of church and state was performed on Jan 1, 2000.
Until 1996 all new-born automatically became members of Svenska Kyrkan. 

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