Which one is correct?
"in northern" or "at Northern"?

Some examples from the web:

• American bombers have attacked synthetic gasoline plants in northern, central, western and eastern Germany.
• Subject: Toll payment devices on motorways in northern Portugal
• He's still in northern Florida.
• There'd been a nuclear incident at a research facility in northern Mongolia.
• My second question concerns Turkey's position with regard to the Kurds in northern Iraq.
• The Union remains in favour of the maintenance of a Kurdish enclave in northern Iraq.
• There's a story like that in northern Europe.
• He just got back from a tour in northern Afghanistan.
• We're the top luxury broker in northern California.
• The American company Chevron has won a tender to start shale gas exploration in northern Bulgaria.
• On 2 September, Human Rights Watch charged Turkey and Iran with killing civilians in northern Iraq.
• Not long ago, when I visited Paredes, in northern Portugal, residents alerted me to the municipality's sewerage problems.
• Cooperatives supply water to residents in various parts of the municipality of Paredes in northern Portugal.
• The Council remains deeply concerned about the conflict in northern Uganda.
• Moreover, the Community contributed ECU 8 m to rehabilitation projects in northern Iraq in 1994/95.
• But planning permission in northern Germany must not be held up by a legal action brought 1500 km further south.
• Benito Mussolini has been hiding out in northern Italy, but he plans an escape to Spain...
• Over the last decade there has been a sharp rise in cancer cases in northern Kosovo.
• This ancient-walled city in northern Italy became a center for a group of doctors determined to find a way to boost cycling performance.
• The Council remains deeply concerned by the situation in northern Uganda and the attacks and atrocities carried out by the 'Lord's Resistance Army' (LRA) in northern Uganda and southern Sudan.

Some examples from the web:

• He saw her at Northern Care.
• Monica Archer was a nurse at Northern Omaha Medical, and she worked pro Bono with disabled veterans at the V.A.
• And you'll have another look at Northern Sky Laboratories.
• Renowned Economics Professor at Northern Cal university.
• PCI Germany internal line between Brunsbüttel-Groβgartach and Wilster-Grafenrheinfeld (DE) to increase capacity at Northern and Southern borders
• Why did you not wait at northern gate as ordered?
• Why did you not wait at northern gate as ordered?
• - I saw you at the Northern Open.
• I just got a call from Louie at the Northern.
• Dr. Rathburn just got in an unmarked Lincoln Town Car at the northern edge of the park.
• Have a taste of our culture like a juicy papaya At the northern-most pyramid built by the Maya.
• Monica Archer called a friend at the Northern Omaha children's hospital about an abandoned 13-year-old boy.
• I'll meet you at the Northern in half an hour.
• Now, with Stawell taken, she has a base at our northern border, which can only mean one thing.
• I understand we're both staying at the Great Northern.
• His mother was a poor immigrant chambermaid at the Great Northern.
• Emergency up at the Great Northern.
• I'll start at the northern edge of the trajectory zone and work my way towards you.
• The mouth of the Gulf is closed by a line commencing at the northern tip of Ra's Musandam and running due east to the coast of Iran.
• Look at these rocks in Northern Scotland.